Home › Blog › Filtration & Venting › The vent and the IP rating
Why an Enclosure Vent Doesn't Carry the IP Rating: Pressure Equalization and Hydrophobic Venting
An ingress-protection rating belongs to the assembled enclosure, not to the venting membrane inside it. A pressure-equalization vent lets a sealed housing breathe as it heats and cools, passing air and water vapor while a hydrophobic ePTFE membrane resists liquid water and dust, and that resistance supports the enclosure's IP rating per IEC 60529. But the rating is earned by the whole assembly in an ingress test, not by any single converted part.
This guide explains pressure equalization, the difference between hydrophobic and oleophobic venting, the pressure-drop versus capture trade in a foam filter, and the failure modes that follow from getting the part right but the system claim wrong.
Request a quote for your project →
The application problem: a sealed box still has to breathe
A sealed outdoor or mobile enclosure faces a contradiction. To keep water and dust out, designers seal it. But a sealed volume of air expands when the housing heats in the sun or under load and contracts when it cools, and that creates a pressure differential across the wall. With nowhere to go, the differential stresses gaskets and seals, can draw moisture past them as the box cools, and can deform thin walls. The enclosure has to stay sealed against liquid and stay open to pressure at the same time.
A pressure-equalization vent resolves this. It seals a small opening in the otherwise-sealed wall with an ePTFE membrane that passes air and water vapor freely while blocking liquid water and dust. The housing breathes, the pressure equalizes, and the membrane keeps liquid out.
The same principle appears across sealed electronics and outdoor equipment, battery packs that must equalize pressure while resisting water and dust, automotive lighting and ADAS sensor housings that must shed condensation, and water-resistant acoustic ports at microphones and speakers.
Why it is challenging: the rating belongs to the system
The hard part is not the membrane. It is keeping the system claim honest. An IP code (for example IP67 or IP68) is a result the assembled enclosure achieves in an ingress test under IEC 60529; road-vehicle ratings including IP69K are evaluated under ISO 20653, and North American enclosures are classed by NEMA Type under ANSI/NEMA 250. The vent membrane is one contributor to that result.
A correctly chosen, hydrophobic venting membrane supports the rating, but the seal around the vent, the gaskets, the housing joints, and the assembly process all determine whether the finished product passes.
That is why a material supplier or a converter cannot hand you an IP rating on a part. H-O converts the membrane and the die-cut adhesive carrier; the device maker validates the assembled enclosure. Claiming the part is "IP67" rather than saying the part "supports an IP67 enclosure design" is one of the most common ways a venting specification gets the engineering right and the compliance language wrong.
Hydrophobic versus oleophobic venting
PTFE is strongly hydrophobic, which is why an ePTFE venting membrane resists liquid water while still passing air and vapor. That handles rain, spray, and immersion-class water exposure. It does not, on its own, handle oils. Oils and many road-spray contaminants have a lower surface tension than water and can wet and pass through a membrane that only repels water, fouling it or breaching the barrier.
For automotive underbody, engine-bay, lighting, and sensor locations exposed to oils and road spray, an oleophobic-treated ePTFE grade adds oil rejection on top of the hydrophobic water barrier. The treatment is a grade-level choice on the Gore ePTFE venting membrane family; the specific airflow and liquid-entry behavior of any grade is confirmed on the manufacturer's current technical data sheet. Specifying a hydrophobic-only membrane where oils are present is a predictable failure: the water barrier holds, the oil barrier was never there.
The pressure-drop versus capture trade in a foam filter
A reticulated foam filter sits at the opposite end of the application. Where a vent is meant to block liquid and pass air, a foam filter is meant to pass the flow and catch particles. It is a depth-loading filter: particles are captured throughout the open cell network, so capture and flow restriction both rise with thickness and with a finer pore grade.
Reticulated foam is graded in pores per inch (PPI). A lower PPI is coarse, open, and low-restriction; a higher PPI is finer and captures smaller particles at a higher pressure drop. There is no free lunch: tightening the grade to catch finer particles raises the pressure drop the fan or blower must overcome, and over-tightening it starves the airflow. The usual rule is to pick the coarsest grade that still meets the capture requirement, then size the open area so the pressure drop stays within budget.
Air permeability of a grade is commonly characterized by the Frazier method under ASTM D737; pressure-drop figures are grade-specific and belong on the manufacturer's airflow data, not on a blog.
Coating tradeoffs: a sortable view
Once the foam grade is set by the capture-versus-airflow trade, the coating is a separate decision driven by the environment. The table below lets you sort the reticulated foam coating options by the attribute you care about. Coatings change surface duty, not pore capture: a coating adds a small pressure drop and does not close the pores.
Reticulated Foam Coating Tradeoffs
| Grade | Durability | UV / outdoor | Flame option | Lowest restriction | Commonly used for |
|---|---|---|---|---|---|
| Uncoated | Lower | Lower | No | Highest | Clean indoor fan or blower screens; lowest pressure drop and cost |
| Acrylic-coated | Medium | UV, not direct elements | No | Slightly lower | Filters that see UV but are not fully weather-exposed |
| PVC-coated | Higher | Outdoor / wipe-clean | Available | Slightly lower | Outdoor and durable filters; speaker covers; dust pre-filters |
| UL 94 HF-1 | Higher | Per grade | UL 94 HF-1 | Slightly lower | Filters inside a flammability-controlled cabinet or enclosure |
Illustrative only; confirm against current material data and a drawing review. Levels are relative and qualitative. Pore grade (PPI), airflow, pressure drop, and any flame classification are confirmed on the manufacturer's current technical data sheet. The coating is a surface-duty choice and does not set particle capture.
Common failure modes
| Failure mode | Root cause | Consequence |
|---|---|---|
| "Rated IP67" on a part | Treating the membrane's water resistance as the enclosure's IP rating; no assembly ingress test | Overstated compliance; the seal, joints, or assembly fail the actual IEC 60529 test |
| Oil-fouled vent | A hydrophobic-only membrane used where oils or road spray are present | The membrane wets and fouls or breaches; an oleophobic grade was required |
| Undersized vent area | Vent open area too small for the enclosure volume and heat-cool cycle | The housing cannot equalize fast enough; pressure stresses the seals |
| Starved airflow on a filter | Pore grade tightened for capture past what the fan can pull | Pressure drop climbs; airflow and cooling fall short of the design point |
| Filter clogs early | Coarse-PPI margin and face area too small for the dust load | Short service interval; a larger face or coarser grade was needed |
How H-O Products helps
H-O Products is a precision die-cut converter. For venting, we convert Gore ePTFE venting membrane (hydrophobic, and oleophobic-treated where oils are present) and the die-cut adhesive ring or carrier that mounts it, cut to your drawing; the assembled enclosure carries the IP rating, which the device maker validates in an ingress test. For filtration, we convert reticulated polyurethane in uncoated, acrylic-coated, PVC-coated, and UL 94 HF-1 flame-rated grades into die-cut filter packs sized to your capture-versus-airflow target.
As an ISO 9001:2015 certified organization, we frame the part honestly: it supports your IP-rated enclosure design rather than carrying the rating itself, and grade properties are confirmed against the manufacturer's current technical data sheet.
Designing a vent for an IP-rated enclosure?
Send us your target IP code and enclosure volume, plus whether oils or road spray are present and the airflow your filter must pass. We will recommend a membrane or foam grade direction and convert samples on your footprint.
Samples typically ship in 3 to 5 business days for common die-cut configurations; standard production runs about two weeks.
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
Does the vent membrane or the enclosure carry the IP rating?
The assembled enclosure carries the IP rating, not the vent membrane. An IP code such as IP67 or IP68 is a result the whole assembly achieves in an ingress test under IEC 60529. A hydrophobic venting membrane supports that result, but the seals, joints, and assembly determine whether the finished product passes, so a converted part should be framed as supporting an IP-rated enclosure design rather than being rated itself.
What is the difference between hydrophobic and oleophobic venting?
A hydrophobic ePTFE membrane resists liquid water while passing air and vapor, which handles rain, spray, and immersion-class water. It does not resist oils on its own. An oleophobic-treated grade adds oil rejection on top of the hydrophobic water barrier, which is needed for automotive underbody, engine-bay, lighting, and sensor locations exposed to oils and road spray.
How does pore grade affect pressure drop in a foam filter?
A reticulated foam is a depth-loading filter, so a finer pore grade (higher PPI) captures smaller particles but raises the pressure drop the fan or blower must overcome, while a coarser grade (lower PPI) is more open and lower restriction. The usual rule is to pick the coarsest grade that still meets the capture requirement, then size the open area so the pressure drop stays within budget.
Request a quote for your filtration & venting part
Send H-O your drawing or describe the part—engineering reviews every RFQ and converts samples on your geometry.
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). IEC.
- ISO 20653 (road vehicles, degrees of protection, including IP69K). ISO.
- ANSI/NEMA 250 (enclosure Type ratings). NEMA.
- ASTM D737 (air permeability) and ASTM E96 (water-vapor transmission). ASTM International.
- UL 94 (flammability). UL Standards.
- Manufacturer technical data sheets: Gore ePTFE venting membrane and reticulated polyurethane filter foam.
This article cites general engineering principles and published standards (IEC 60529 for ingress protection, ISO 20653 for road-vehicle IP including IP69K, ANSI/NEMA 250 for NEMA Type enclosures, UL 94 for flammability, ASTM D737 for air permeability, ASTM E96 for water-vapor transmission). Material names refer to material families H-O Products converts.
Airflow, pressure drop, and liquid-entry values are grade-specific; confirm all values against the manufacturer's current technical data sheet and an engineering drawing review.
An IP or NEMA rating is achieved by the assembled enclosure, not by a converted part; H-O does not certify the finished enclosure or device.