How to Design Silicone Gaskets for IP67 and IP68 Waterproof Enclosures

A waterproof enclosure needs continuous sealing contact around the joint. Even a suitable silicone gasket can leak if the housing flexes between screws or the seal shifts during assembly. Review how the groove and fasteners control compression, including the effect of manufacturing tolerances.

This becomes increasingly important when a product must meet IP67, IP68 or other demanding ingress-protection requirements in production rather than only passing a prototype test. Engineers therefore need to treat waterproofing as a mechanical sealing system. Material selection is part of that system, but gasket geometry, enclosure stiffness, compression control, screw layout, pressure equalization and manufacturing consistency often determine whether the design remains reliable over thousands of assembled units.

This guide focuses on silicone gasket and enclosure design from that perspective. It covers the practical differences between O-rings, custom molded gaskets and overmolded seals, as well as the mechanical details that influence long-term waterproof performance.

Understanding IP Ratings

Ingress Protection ratings describe how effectively an enclosure prevents solids and water from entering. The familiar IP code contains two digits. The first describes protection against solid objects and dust, while the second describes protection against water.

For waterproof electronic products, several ratings are particularly common:

IPX6: protection against powerful water jets.
IPX7: protection during temporary immersion under specified test conditions.
IPX8: protection during continuous immersion under conditions defined for the product and application.
IPX9K: protection against high-pressure, high-temperature water jets.

IPX8 should not be interpreted as a universal fixed depth or duration. The actual immersion conditions need to be defined for the product.

This distinction matters because different tests create different loads on the enclosure. A design that performs well during immersion may not necessarily perform equally well against high-pressure jets. Similarly, an enclosure that survives a short laboratory test may still develop moisture problems after repeated temperature cycling, aging and field use. The sealing concept should therefore be selected according to the real operating environment rather than the IP number alone.

Waterproof Sealing is a System

The basic function of a gasket is simple: it fills the interface between two surfaces and creates sufficient contact pressure to block a leakage path. In practice, maintaining that contact pressure is more difficult than it appears.

Several variables work together:

gasket hardness and cross-section;
groove width and depth;
enclosure wall thickness and stiffness;
fastener spacing and screw preload;
molded-part flatness and dimensional tolerance;
assembly consistency.

The gasket must be compressed enough to accommodate surface irregularities and dimensional variation, but not so heavily that it becomes excessively distorted, extrudes from its groove or develops unnecessary long-term compression set. At the same time, the enclosure must be stiff enough to keep the compression relatively uniform along the entire sealing path. The fasteners must then provide enough clamping force without damaging the plastic housing or creating excessive local deformation.

These variables cannot be designed independently. A softer gasket may tolerate more housing variation, for example, but it can also be easier to displace during assembly. A stiffer gasket may provide higher local reaction force, yet require a stronger housing and more controlled clamping.

For this reason, a good waterproof design begins with the complete sealing architecture rather than with a material specification such as “50 Shore A silicone.” When the sealing path cannot be handled by a standard component, a gasket can be designed around the enclosure geometry, compression requirement and assembly conditions instead.

O-Rings, Custom Molded Gaskets and Overmolded Seals

There are several practical ways to seal an enclosure, and each has advantages depending on geometry, production volume, assembly method and service requirements.

O-Rings

O-rings are highly effective when the sealing path is simple and the groove can be designed specifically around a standard or customized circular cross-section. They are widely used because their sealing behavior is well understood, and many applications can be served without developing a complex gasket geometry. In well-designed automated or controlled assembly systems, O-rings can also be used reliably in high-volume production.

The difficulty appears when the enclosure has a complex perimeter, multiple screw holes, irregular corners or local sealing features. A long O-ring can twist, stretch or lift from the groove during assembly if retention is poor. The operator may also have difficulty confirming that the seal is correctly seated before the enclosure is closed.

O-rings are therefore particularly attractive when:

the sealing path is simple;
a suitable cross-section is available;
the groove provides reliable retention;
assembly can be adequately controlled.

For irregular electronic enclosures, however, a custom molded gasket often gives the designer more control over the sealing geometry.

Custom Molded Gaskets

A molded silicone gasket can follow the exact perimeter of an enclosure and incorporate features that would be difficult to achieve with a standard O-ring.

Typical integrated features include:

screw-hole sealing rings;
locating tabs;
retaining features;
local sealing beads;
different widths or cross-sections around the same gasket.

This can simplify assembly because the gasket naturally fits one specific orientation. It also allows engineers to control compression differently around critical areas such as connectors, corners or screw bosses. Instead of asking one uniform O-ring section to perform every sealing function, the gasket geometry can be adapted to the local enclosure structure.

Molded silicone gaskets are therefore particularly useful for electronics housings, automotive modules, industrial controls, handheld devices and other enclosures with non-circular sealing paths. Depending on geometry, production volume and dimensional requirements, these parts can be manufactured through compression molding or LSR molding.

The main trade-off is that a custom gasket requires dedicated tooling and still remains a separate component during final assembly. Retention and positioning must therefore be considered during the enclosure design.

Overmolded Seals

When assembly consistency becomes a major concern, integrating the seal directly onto one enclosure component can provide another level of process control. With overmolding, silicone can be molded onto a compatible plastic or metal substrate so that the sealing element becomes part of the component itself.

The main advantages are:

fewer loose components during assembly;
reduced gasket positioning errors;
less risk of twisting or stretching;
more repeatable seal location;
easier high-volume assembly.

The biggest advantage is not simply that the gasket cannot be lost. The more important benefit is reduction of assembly variation. Operators no longer need to manually position a loose gasket around a complex perimeter, and there is less opportunity for the seal to become partially trapped between enclosure halves.

Overmolding is not automatically the best option for every waterproof enclosure because it introduces additional tooling, substrate compatibility, bonding or mechanical-retention requirements and tighter process control. However, for complex sealing paths and products that require high repeatability, it can significantly simplify final assembly.

Gasket Compression

A silicone gasket seals because the enclosure compresses it against the mating surfaces. Without sufficient compression, small gaps can remain between the gasket and housing, especially where molded components are not perfectly flat. Excessive compression, however, can create a different set of problems.

If the gasket is squeezed too heavily, the silicone must move somewhere. Depending on the groove design, it may bulge sideways, distort around corners or generate higher loads than the plastic housing can support. Excessive long-term compression can also reduce the gasket’s ability to recover after aging or repeated opening and closing.

A practical gasket design therefore aims for controlled rather than maximum compression. The target depends on factors such as:

silicone hardness;
gasket cross-section;
compression-set performance;
enclosure stiffness;
environmental exposure;
expected service life.

For example, a 2.0 mm gasket compressed to approximately 1.5 mm is experiencing meaningful compression, but that dimensional relationship alone does not prove that the seal is correct. Engineers still need to consider tolerances on the gasket, groove, enclosure surfaces and fastener system.

A design that appears correct at nominal dimensions may become under-compressed at one tolerance extreme and over-compressed at another. This tolerance stack becomes particularly important in molded plastic housings because flatness and warpage can vary across large parts. Waterproof sealing should therefore be evaluated using realistic production tolerances rather than nominal CAD geometry alone.

Designing the Gasket Groove

The groove performs several functions at the same time. It locates the gasket, controls its compressed height and prevents excessive lateral movement. A poorly designed groove can allow a gasket to roll, bulge or shift before the housing is fully assembled.

One reference design uses a groove approximately 1.8 mm wide and 1.0 mm deep in a wall with an overall thickness of roughly 2.4 mm. A narrow retaining skirt remains beside the groove to help contain the gasket as pressure is applied. These dimensions should not be copied directly into another product, but the underlying principle is important: the groove should provide enough lateral support to keep the gasket stable during compression.

A practical groove design should provide:

sufficient depth to establish the intended gasket compression;
enough lateral space for controlled deformation;
adequate retention during assembly;
smooth transitions around corners;
geometry that can be manufactured reliably.

Silicone is nearly incompressible in bulk, which means that when its height is reduced, the material tends to expand sideways. The groove therefore needs enough space for controlled deformation without becoming so wide that the gasket loses position.

Corners deserve particular attention. Very sharp changes in direction are more difficult to mold, assemble and compress uniformly. Smooth radii normally make the sealing path easier to manufacture and reduce local stress concentration in both the gasket and enclosure.

The groove must also be designed with tooling in mind. Deep narrow channels, difficult undercuts or poorly accessible sealing surfaces may make both plastic molding and silicone molding more difficult. Waterproof performance and moldability should therefore be reviewed together during DFM rather than treating the gasket groove as a late-stage addition to an existing housing.

Sealing Beads

A flat gasket surface does not always produce the most reliable seal. Molded silicone gaskets can incorporate raised sealing beads or compression ribs that concentrate clamping force into smaller contact areas.

These features are particularly useful around:

screw holes;
connectors;
enclosure corners;
long spans between fasteners;
other locations where available clamping force is relatively low.

A narrow bead can create higher local contact pressure than a broad flat surface under the same overall fastener load. When designed correctly, this allows the gasket to accommodate small surface variations without requiring excessive compression across the entire part.

Some waterproof enclosure designs use relatively narrow ribs around screw locations and dual sealing ribs around the outer perimeter. The concept is to create controlled high-pressure sealing lines rather than relying solely on the entire gasket surface.

This approach also gives engineers another tool for managing housing flexibility. Areas close to screws naturally receive more clamping force, while areas midway between screws often receive less. Gasket geometry can partly compensate for this difference, although it cannot replace adequate enclosure stiffness and fastener placement.

The exact rib geometry should be selected carefully. Extremely sharp features can be more difficult to mold consistently, while oversized ribs may create unnecessary assembly force. The design should consider silicone hardness, mold filling, flash control, tooling capability and the expected compression range.

If the enclosure also includes electrical or cable interfaces exposed to water and dust, the connector gasket should be evaluated as part of the same sealing system rather than treated independently from the enclosure gasket.

Fastener Spacing

Fasteners do more than hold the enclosure together. They establish the clamping force that creates the seal.

Near a screw, the enclosure halves are pulled firmly together. As the distance from the screw increases, the housing can flex away from the gasket, especially if the plastic wall is thin or the enclosure has a large unsupported span. The result is a reduction in gasket compression between fasteners.

This is one of the reasons a waterproof enclosure can leak even when the gasket itself appears correct. The problem may not be the seal material at all; it may be mechanical deflection of the housing.

One practical enclosure design uses fastener spacing of approximately 35 mm or less as a starting point for higher sealing requirements. This should be treated as an engineering reference rather than a universal IP67 or IP68 rule. Acceptable spacing depends on:

housing material and stiffness;
wall thickness;
enclosure geometry;
gasket hardness;
sealing-bead geometry;
compression level;
screw preload.

A thick glass-filled engineering plastic housing may tolerate a larger unsupported span than a thin ABS enclosure. Similarly, a narrow gasket with a concentrated sealing bead may react differently from a wide flat gasket.

Finite element analysis can be useful for demanding designs, but prototype pressure or immersion testing remains important because real molded-part warpage and assembly variation may not be fully captured in the model.

Adding another screw is often less expensive than trying to correct an enclosure that repeatedly leaks between widely spaced fasteners. Fastener layout should therefore be established early in the mechanical design rather than being decided only after the electronics and industrial design are complete.

Screw Selection and Plastic Boss

The screw and boss system must generate reliable clamping force without damaging the enclosure. Thread-forming screws for plastic are often preferred because they create threads in the polymer rather than requiring a separate nut or insert.

Trilobular thread-forming screws are one example. Their geometry is designed to form a secure thread while reducing some of the stresses associated with conventional thread cutting. Torx drives can also be useful in production because they provide good tool engagement and are compatible with manual or automated assembly.

A reference design uses an M2 thread-forming screw with a pilot hole in the approximate range of 1.4 to 1.55 mm. This value should not be treated as a universal specification. The correct pilot-hole diameter depends heavily on the screw supplier, thread geometry, plastic material, molding shrinkage and boss dimensions.

The most important variables to verify include:

installation torque;
stripping torque;
pull-out strength;
boss cracking or hoop stress;
long-term clamp-load retention.

A pilot hole that is too small can generate excessive hoop stress and crack the boss. A hole that is too large can reduce thread engagement and pull-out strength. The final design should therefore be verified using the actual production resin and screw.

The screw head also influences sealing performance. A head or washer geometry that distributes load over a larger area can reduce local damage to the plastic and help maintain clamping force. For waterproof housings, long-term torque retention should be considered as well because polymer creep can gradually reduce clamp load.

Screw Holes

Every opening through the enclosure deserves attention, including screw holes. If a screw passes through or close to the sealed cavity, the design may require an independent sealing feature around the boss.

A molded gasket can incorporate a ring around each screw hole so that tightening the enclosure simultaneously compresses both the perimeter seal and the local screw-hole seal. This is one reason custom molded gaskets can be attractive for complex housings: several sealing functions can be integrated into one part.

The enclosure geometry around the boss should also support the gasket. A small retaining wall or skirt can prevent the silicone from being pushed away from the sealing area when the screw is tightened. The aim is to create repeatable local pressure rather than allowing the gasket to deform unpredictably around the boss.

If the screw remains completely outside the sealed cavity, the design may be simpler. However, the mechanical relationship between screw location and perimeter gasket compression still needs to be considered.

Enclosure Corners and Parting Surfaces

Sharp enclosure corners often create difficulties for both molding and sealing. The gasket must turn through a tight radius, the plastic housing may be more prone to stress concentration, and uniform compression becomes harder to maintain.

Using reasonable corner radii improves both gasket molding and assembly. The seal can follow the enclosure more naturally, and the groove is less likely to create local pinching or stretching.

The mating surface itself should also be examined carefully. Potential problems include:

mold parting lines crossing the sealing path;
gate vestiges near gasket contact areas;
sink or local surface deformation;
enclosure warpage;
abrupt changes in sealing-surface height.

Where possible, critical sealing surfaces should be kept away from mold features that are difficult to control.

A small intentional step between enclosure halves can also help manage the visible joint line and make the product appearance more consistent. Industrial design and waterproofing do not need to conflict, but the joint should be designed deliberately rather than allowing tooling limitations to determine the final sealing surface.

Temperature Changes

Waterproof products do not operate at constant temperature. Outdoor electronics may heat in direct sunlight and cool rapidly after rain. Automotive modules experience repeated thermal cycles. Handheld devices can move between air-conditioned indoor environments and hot, humid outdoor conditions.

When the air inside a sealed enclosure heats up, it expands and internal pressure rises. If the housing or seal allows a small amount of air to escape, the pressure may equalize. When the enclosure later cools, the internal air contracts and pressure falls. The resulting pressure difference can pull external air back toward the enclosure.

If that incoming air contains moisture, even a very small leakage path can gradually introduce humidity. This is why a product may show internal condensation or corrosion even though it was never visibly submerged.

Several approaches are commonly considered:

improve the primary gasket sealing system;
use a hydrophobic vent or pressure-equalization membrane where appropriate;
reduce unnecessary internal pressure peaks;
avoid relying on desiccant as the primary moisture-control method.

A hydrophobic vent can reduce pressure differences while resisting liquid water entry, but the vent itself becomes another engineered component. It must remain clean and correctly positioned, and its airflow capacity must be appropriate for the enclosure volume and rate of temperature change.

Desiccant can help manage moisture temporarily, but it should not be treated as a substitute for a correctly designed sealing system. Once the desiccant absorbs enough moisture, its effectiveness decreases, while the underlying ingress mechanism remains.

Material Selection

Geometry and compression are critical, but the silicone compound must also match the operating environment.

General-purpose silicone rubber is widely used for enclosure gaskets because it combines flexibility with broad temperature capability and good resistance to weathering and ozone. It is particularly useful where the gasket must remain elastic through repeated thermal cycling.

However, standard silicone is not ideal for every chemical environment. Exposure to fuels, oils or aggressive fluids may require fluorosilicone or another elastomer. In automotive or industrial applications, the fluid environment should therefore be reviewed alongside the IP requirement.

Important material-selection factors include:

operating temperature;
exposure to oils, fuels or chemicals;
required hardness;
long-term compression set;
environmental aging;
regulatory requirements where applicable.

Hardness also affects sealing behavior. Softer silicone can conform to surface irregularities with relatively low clamping force, which is useful for lightweight plastic housings. Harder silicone can resist deformation and provide stronger reaction force, but may require a stiffer enclosure and more carefully controlled compression.

For a new enclosure project, hardness should not be selected only from a supplier’s standard material list. It should be considered together with gasket section size, groove depth, available screw force and the flexibility of the mating housing.

Compression Molding or LSR Injection Molding?

Both HCR compression molding and liquid silicone rubber injection molding can be used for waterproof gaskets, but the best process depends on part geometry, volume and required manufacturing control.

Compression molding can be effective for many custom silicone gaskets, particularly when volumes are moderate and the geometry is relatively straightforward. Tooling can sometimes be simpler, and a wide range of solid silicone compounds and hardness levels can be processed.

LSR injection molding becomes especially attractive for higher-volume parts, thin or complex gasket geometries and applications where automated production and repeatable material dosing are important. It is also commonly considered when the seal will be integrated through overmolding.

The process decision should consider:

gasket geometry and cross-section;
annual production volume;
dimensional repeatability;
flash sensitivity;
automation requirements;
insert or substrate integration;
tooling investment.

The process decision should not be separated from part design. Very thin sealing ribs, narrow flow paths, undercuts, flash-sensitive surfaces and insert bonding requirements can all influence the appropriate mold concept. A gasket designed without considering the molding process may later require unnecessary compromises in tooling or production.

Flash Control

Silicone flash may appear small, but on a sealing surface even a thin irregular feature can alter contact pressure or interfere with gasket seating.

The mold parting line should therefore be positioned carefully. Ideally, it should not cross the most critical sealing bead where uncontrolled flash could create a leakage path. Tooling accuracy, shut-off design and molding process stability all contribute to flash control.

For custom molded gaskets, designers should pay particular attention to:

sealing-bead parting-line location;
flash thickness and consistency;
narrow rib geometry;
deflashing method;
dimensional stability after post-processing.

Deflashing methods that are acceptable for a general silicone component may not be suitable if they damage a narrow sealing rib or change the cross-section.

This is another reason why gasket design and tooling design should be reviewed together. A CAD model can show a theoretically perfect sealing bead, but the manufacturing process must be capable of reproducing that geometry consistently. Early tooling and DFM review can identify difficult shut-offs, flash-sensitive sealing surfaces and moldability problems before production tooling is finalized.

Overmolding Can Reduce Assembly Variation

The commercial case for overmolding becomes clearer when total manufacturing cost is considered rather than tooling cost alone.

A loose gasket requires molding, handling, storage, placement and inspection. If operators must stretch the gasket around corners or manually fit it around multiple screw bosses, assembly time increases and the opportunity for errors grows. A misplaced seal may not be obvious after the enclosure is closed, which means the defect may only appear during leak testing or, worse, in the field.

Overmolding removes several of these variables by fixing the seal to the substrate during manufacturing. The geometry and location of the sealing element are defined by the mold rather than by the assembler.

However, successful overmolding introduces its own engineering requirements:

reliable silicone-to-substrate retention or bonding;
suitable substrate material;
controlled shut-off areas;
stable insert positioning;
effective flash control;
complete filling of the sealing geometry.

For these reasons, overmolding is most attractive when assembly simplification, consistency and field reliability justify the additional tooling and process development.

Do Not Design Only for the First IP Test

One of the most common mistakes in waterproof product development is optimizing the prototype until it passes a single IP test and then assuming that production will perform the same way.

Production introduces variation. Silicone hardness can vary within specification. Molded gasket dimensions vary slightly. Plastic housings warp. Screw torque changes between assembly tools. Operators handle components differently. Mold wear can gradually affect flash and dimensions.

The sealing system should therefore tolerate normal variation in:

gasket dimensions;
groove dimensions;
housing flatness;
screw torque;
material hardness;
molded-part warpage;
flash condition.

This does not mean simply increasing gasket compression. A better approach is to control the entire tolerance stack and identify which dimensions most strongly influence sealing performance. Groove depth, gasket height, housing flatness and screw preload are often more important than cosmetic dimensions elsewhere on the product.

Validation should also reflect the intended life cycle. Depending on the application, this may include repeated assembly, thermal cycling, aging, chemical exposure, vibration or pressure changes before repeating the ingress test.

Passing IP67 on a fresh prototype is useful. Passing it consistently after realistic manufacturing and environmental variation is a much stronger indication that the enclosure has been designed correctly.

Designing a Reliable IP67/IP68 Sealing System

The most reliable waterproof enclosures are rarely the result of one exceptional component. They are the result of several ordinary engineering decisions working together correctly.

The silicone compound must suit the temperature and chemical environment. The gasket geometry must create predictable compression. The groove must retain the seal. The enclosure must remain stiff between fasteners. Screw locations must provide adequate clamping force. Tooling must control flash and dimensional variation. The assembly process must reproduce the same condition repeatedly.

For simple products, an O-ring may provide everything that is needed. For irregular housings, a custom molded silicone gasket provides greater control over the sealing path and local compression. For higher-volume assemblies where gasket placement becomes a major source of variation, silicone overmolding may offer a more integrated solution.

Fecision develops custom silicone seals and selects the manufacturing route to suit the assembly. During DFM, we check how the gasket fits the groove and where the housing controls compression. Tooling review then addresses flash and dimensional variation so the approved seal can be reproduced in production.