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Sealing, Cushioning or Venting? Choosing Materials for ADAS Sensor Housings
A radar, LiDAR, camera or sensor-fusion ECU housing is a small enclosure with four different material jobs: an environmental seal that closes the joint toward an ingress class, a cushion that protects the board and optics, an EMI gasket that keeps the enclosure shielding as one body, and a pressure vent that lets the sealed box breathe. The four jobs point at four families, closed-cell silicone, microcellular polyurethane, conductive silicone and microporous ePTFE, and confusing them costs either the seal, the shield or the optics.
This guide separates the jobs, maps the families, and ends with a selector that turns your housing location into a cautiously framed direction.
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The application problem: one housing, four material jobs
An exterior sensor lives in sun, road spray, ozone and a wide temperature swing while its electronics demand a dry, stable, electromagnetically quiet interior. That translates into four distinct duties at the design level:
- Environmental sealing: a resilient, usually non-conductive gasket closes the housing joint against water and dust toward an ingress class under IEC 60529, including the road-vehicle IP6K9K variant for high-pressure wash exposure.
- Cushioning and gap take-up: a soft pad protects the PCB, the optic and the connector from vibration and tolerance stack-up at low closure force.
- EMI gasketing: a conductive gasket maintains electrical contact across the seam so the enclosure shields as one body, supporting the module's emissions limits under CISPR 25.
- Pressure venting: a microporous membrane lets the sealed housing equalize internal pressure as temperature and altitude change, while staying sealed to liquids.
The same module frequently carries all four parts, each die-cut to its own geometry.
Why the choice is challenging: the jobs pull in opposite directions
Sealing and venting are literal opposites: the seal exists to keep everything out, and the vent exists to let air through on purpose. A perfectly sealed housing builds and releases pressure every heat cycle, which stresses the gasket and can pump moisture past the seal or fog an optic, so the right design is a good seal plus a correctly sized vent, not the tightest possible seal.
Sealing and shielding pull apart on chemistry: an environmental gasket is selected for resilience and weathering, while an EMI gasket is selected for conductivity, and a conductive grade is priced for its shielding. Cushioning pulls on a fourth axis, force-deflection at low stress, where a sealing-grade silicone may be firmer than a delicate optic wants. The selection question is therefore not "which material is best" but "which job does this seam or pad actually do," answered location by location.
Recommended material families
Each job maps to a family H-O Products converts. Grade-level values such as compression-deflection, temperature range and flame classification are confirmed against the manufacturer's current technical data sheet before specifying.
For the environmental seal: closed-cell silicone sponge
BISCO® HT and BF closed-cell silicone holds a resilient seal across the widest temperature span of the families here and resists weather and ozone, which makes it the lead for exterior sensor housings and hot, forward-mounted modules. Cellular-silicone properties are characterized per ASTM D1056, and specific grades reach UL 94 flame classifications; confirm the type, class and any flame requirement on the grade data sheet.
For board and optic cushioning: microcellular polyurethane
PORON® microcellular polyurethane holds a controlled, relatively flat force-deflection curve at low stress and recovers without taking a fast set, characterized per ASTM D3574 with compression set per ASTM D395. That makes it the choice for protecting boards and optics, taking up tolerance gaps, and lightly sealing interior seams at low closure force.
For the shielded seam: conductive silicone
SSP502 conductive EMI silicone, available as the die-cut 2368 conductive silicone (SSP502 family), keeps electrical contact across a joint so the enclosure shields as one body, supporting the module's emissions limits under CISPR 25, and conductive grades double as an environmental gasket. The shield rating belongs to the tested assembly, so the joint design is reviewed together with the material.
For pressure equalization: ePTFE membrane
ePTFE pressure-venting membrane is breathable to air but sealed to liquids, so a small die-cut vent patch over a port relieves heat-cycle pressure and reduces condensation while keeping water and dust out. The vent complements the housing seal rather than replacing it; the membrane grade, airflow and water-entry behavior are confirmed against the data sheet for the port size.
Seal, Cushion, Shield or Vent: Material Direction Selector
A resilient closed-cell silicone closes the housing joint toward the ingress class and holds its properties across a wide temperature span with weather and ozone resistance; the joint design completes the seal.
Illustrative only; confirm against current material data and a drawing review. This selector returns a material family direction, not a grade or a guaranteed performance value. Compression-deflection, temperature range, flame classification, conductivity and vent airflow are confirmed on the manufacturer's current technical data sheet, and IP and emissions results belong to the tested housing and module per IEC 60529 and CISPR 25.
Design and converting considerations
- The gasket is one element of the IP rating. The groove geometry, bolt pattern and torque, surface finish and the compressed gasket together reach the class under IEC 60529; the rating belongs to the tested housing. Send the joint detail with the target class.
- Size the vent to the housing. The housing volume and the temperature swing set the vent area; the vent patch is die-cut, adhesive-backed and placed over a port.
- Decide one part or two for seal-plus-shield. A combined conductive gasket simplifies the build; separate parts let each seam be optimized. Define the sealing class and the shielding need together.
- Cushion at low closure force. Optic and board cushions work without pre-loading the housing; specify the gap, the tolerance and the available force so the curve can be matched.
- Process fit. These parts are die-cut, kiss-cut, laser or waterjet cut, laminated and supplied adhesive-backed on liners, sized to the housing geometry and kitted for assembly.
Common failure modes
| Failure mode | Root cause | Consequence |
|---|---|---|
| Fogged optic, pumped moisture | A perfectly sealed housing with no pressure vent | Heat cycles stress the seal and pull humid air past it; add a correctly sized ePTFE vent |
| Seal fails the temperature span | A commodity foam where exterior heat and cold govern | Lost resilience at the extremes; closed-cell silicone was the call |
| Emissions failure at the seam | A non-conductive gasket in a seam that had to carry the shield | The enclosure no longer shields as one body; a conductive silicone gasket supports CISPR 25 compliance |
| Conductive gasket where none was needed | Shielding specified for a seam that only needed sealing | A part selected and priced for conductivity doing a sealing job; split the functions |
| Crushed or set cushion | A firm sealing grade used as an optic cushion | Pre-loaded optic and lost recovery; a soft microcellular polyurethane was the fit |
| IP claim hung on the gasket alone | Rating treated as a material property | An unsupported claim; the class belongs to the tested housing per IEC 60529 |
How H-O Products helps
H-O Products is a precision die-cut converter serving EV and battery programs. We convert closed-cell silicone, microcellular polyurethane, conductive silicone and ePTFE membrane into housing seals, cushions, EMI gaskets and vent patches, cut to your housing geometry. As an ISO 9001:2015 certified organization, we help you define the job at each location, recommend a family and grade direction, and decide whether a seam needs one combined part or two.
We do not produce the raw silicone, foam or membrane; grade values are confirmed against the manufacturer's current technical data sheet, and the IP and emissions results belong to your tested housing and module.
Mapping gaskets onto a sensor module?
Tell us the job at each location, the target ingress class, the temperature span, and whether the module must meet CISPR 25. We will recommend a family and grade direction and convert samples on your geometry.
Samples typically ship in 3 to 5 business days for common die-cut configurations; standard production runs about two weeks; special orders are quoted to the job.
Family-owned in Winsted, Connecticut since 1971 · ISO 9001:2015 certified · OEMs worldwide send us a drawing — and get back their part.
Related reading
Frequently asked questions
What is the difference between an environmental seal and an EMI gasket?
An environmental seal is a resilient, usually non-conductive gasket that closes a housing joint against water and dust toward an ingress class under IEC 60529; it is chosen for its sealing and weather resistance. An EMI gasket is electrically conductive and maintains contact across a seam so the enclosure shields as one body, supporting the module's emissions limits under CISPR 25. A conductive silicone gasket can do both jobs in one part, which is common on sensor-fusion ECUs.
Why not just seal a sensor housing completely instead of adding a vent?
A perfectly sealed housing builds and releases pressure every heat cycle, which stresses the gasket and can pump moisture past the seal or fog an optic. A small ePTFE membrane vent patch is breathable to air but sealed to liquids, so it equalizes pressure and reduces condensation while keeping water and dust out. The vent complements the housing seal rather than replacing it; size the vent from the housing volume and the temperature swing.
How does a die-cut gasket relate to an IP rating like IP67 or IP6K9K?
The gasket is one element of the sealed joint, not the rating by itself. An ingress class under IEC 60529, or the road-vehicle IP6K9K variant, is achieved by the whole joint: the groove geometry, the bolt pattern and torque, the surface finish, and the compressed gasket. A correctly sized closed-cell silicone gasket in a well-designed groove lets the joint reach a high class, but the rating belongs to the tested housing.
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Last updated · Reviewed by H-O Products engineering (ISO 9001:2015 certified converter, Winsted, CT).
References
- IEC 60529, Degrees of Protection Provided by Enclosures (IP Code). International Electrotechnical Commission.
- CISPR 25, Vehicles, boats and internal combustion engines: radio disturbance characteristics, limits and methods of measurement for the protection of on-board receivers. CISPR / IEC.
- ASTM D1056, Standard Specification for Flexible Cellular Materials: Sponge or Expanded Rubber. ASTM International.
- UL 94, Standard for Tests for Flammability of Plastic Materials for Parts in Devices and Appliances. UL Standards.
This article cites general engineering principles and published standards (IEC 60529 for ingress protection, CISPR 25 for vehicle-component emissions, ASTM D1056 for cellular rubber and silicone, ASTM D3574 and ASTM D395 for urethane force-deflection and compression set, UL 94 for flammability). Material names refer to material families H-O Products converts.
Compression-deflection, temperature, conductivity, flame and vent-airflow values are grade-specific; confirm all values against the manufacturer's current technical data sheet and an engineering drawing review.
IP classes and emissions results belong to the tested housing and module. All parts are custom manufactured to order and minimum production run quantities apply. H-O is a die-cut converter, not a raw-material producer, and does not certify the finished assembly.