IP67 vs IP68: What Vent Membrane Rating Do You Need?

The IP rating on a vent membrane datasheet is the single most misunderstood number in electronics protection, because it describes the membrane and the housing are described separately. A design team reads IP68 on a membrane, assumes the enclosure inherits it, and then discovers at the test house that the enclosure is the part that was never rated. The other half of the misunderstanding is that IP67 and IP68 are treated as a ladder, when they are in fact two different test conditions sitting side by side in the same standard.

This article works through both, using our own published product data for the ePTFE protective vent membranes and the specification published for our IP-rated electronics vent membranes. The rating definitions come from the international standard itself, linked below rather than paraphrased.

IP67 and IP68 are two tests, not two grades of one

The IP code is built from two independent digits under IEC 60529: the first covers solids, the second water. So IP67 means dust-tight plus a specific immersion test, and IP68 means dust-tight plus a different, deeper and longer immersion condition.

The water side is where the two diverge, and the divergence is the whole point. IPX6 is protection against powerful water jets. IPX7 is immersion in water up to 1 m for up to 30 minutes. IPX8 is continuous immersion, and the standard deliberately leaves the depth and duration to be agreed between the manufacturer and the customer, because a housing designed for a shallow, brief immersion is a different design from one meant to stay submerged. IPX9K, which appears in our own published range, is protection against high-pressure, high-temperature water jets.

Because IPX8 is an agreement rather than a fixed condition, so a product marked IP68 tells you the manufacturer has an agreed continuous-immersion condition, and it tells you nothing about the depth or duration until that agreement is attached, so the useful question is not whether the part is IP68 but under which agreed conditions it was tested.

The solids digit matters just as much for a vented enclosure. IP6X, dust-tight, is a requirement on the housing and its interfaces: a vent membrane will pass particles while it is doing its job, but it cannot stop dust entering through a housing joint. Vehicle-mounted equipment has its own version of the same code, published as ISO 20653, and it is worth checking which of the two documents the customer contract references.

The enclosure rating and the membrane rating are different numbers

Here is the sentence that prevents most of the wasted engineering time: a membrane published as IP67/IP68 does not make the enclosure IP67/IP68. An enclosure inherits its rating from the enclosure body, the thread or flange interface, the seal and the assembly process. The membrane is one component inside that system, and it can only ever be as good as the interface it is mounted into.

What the membrane actually does is well described in our own published feature set. It is waterproof and breathable at the same time, forming an impassable barrier to liquids while allowing moisture vapour and air through. It balances the pressure differential between the inside and the outside of the device, so that internal pressure is equalised instead of building up, and it does so while blocking water and other contaminants.

That is the point worth understanding for a sealed box. Because a housing that cannot equalise pressure either traps it or draws condensation, so the failure mode of a sealed enclosure is often not water getting in but air and moisture getting in from the inside, so venting is a control on the failure mode rather than a replacement for sealing. Damp-heat behaviour of this kind is assessed separately under IEC 60068-2-78, and it is a different test from the immersion rating entirely.

Decoding our published vent table

Our published product specification for the protective vent membrane range is unusually complete, and it is worth reading as a set of trade-offs rather than as a menu.

Four things fall out of that table. The water entry pressure is a different metric from the IP rating, and it converts directly: 10 psi is about 0.69 bar, 14.5 psi about 1.0 bar, 21 psi about 1.45 bar, 29 psi about 2.0 bar, 43.5 psi about 3.0 bar, 58 psi about 4.0 bar and 80 psi about 5.5 bar. That number tells you how much pressure the membrane resists before liquid starts to pass, which is useful when you know the depth of immersion and the density of the liquid, and it is not the same thing as the immersion rating on the same row.

Second, airflow is quoted at 70 mbar, and that reference pressure is what makes the figures comparable between models. High-flow models such as SR132 and SR135 sit at 4000–5000 and 3500–4000 ml/min/cm², while the high-pressure models trade airflow for resistance: SW002 gives 100–200 ml/min/cm² at 58 psi, and SD221 gives 800–1000 ml/min/cm² at 80 psi. Third, the IP column is not a single number across the range: SR450 is published IP68 only, SR455 is published IP68/IP69K, and the rest are published IP67/IP68. Fourth, the temperature band changes the part you can use, with the SW series published from −100 to 250℃ against −40 to 125℃ for the SR and SD series.

Die-cut geometry is published as well, from 2.8 × 1.0 mm up to 40.0 × 19.5 mm, with part counts across four series (SR, SD, SP and SW), and a self-adhesive venting membrane format is offered alongside the encapsulated styles.

Choosing between them by exposure

With the two ratings separated, the decision becomes an exposure question rather than a preference.

If the enclosure sees splash, rain, dust and occasional short immersion, IP67 on the assembly is the meaningful target, and the published membrane range covers it with the IP67/IP68 models. If it can be submerged and stay submerged, the target becomes IP68, and the conditions — depth, duration, and the liquid involved — have to be written down, because that is what IPX8 is agreed to mean. If the exposure is pressure-driven water rather than immersion, the published IP69K option on SR455 is the relevant row, since IPX9K is a jet test rather than an immersion test.

Vehicle-mounted and outdoor equipment add their own dimensions. Equipment in a road or off-road environment is usually specified against ISO 20653 rather than plain IEC 60529, and cold-soak or damp-heat exposure is a separate assessment under IEC 60068-2-78, so the temperature band of the membrane matters as much as its IP line. And for many products — indoor enclosures, control cabinets with filtered ventilation, sealed instruments inside a dry building — IP65 or IP54 is the honest requirement, in which case specifying IP68 for the membrane is paying for a capability the installation will never test.

Media compatibility and the operating envelope

The remaining published features decide whether a given membrane survives its environment. Chemical corrosion resistance protects components from the chemicals and solvents common in industrial duty. UV protection blocks solar radiation and prevents yellowing and performance loss over long outdoor exposures. Dust and oil resistance combine particle blocking with oil repellency, which is what the oleophobic grade in the specification refers to, and it matters where a housing is exposed to lubricant spray or road salt film.

High-temperature resistance is published as a separate feature because heat is what degrades a membrane fastest, and the two temperature bands in our range, −40 to 125℃ for the SR and SD series and −100 to 250℃ for the SW series, are not interchangeable in a hot enclosure. The practical sequence is to pick the exposure, pick the IP line that exposure implies, then pick the membrane inside that line on airflow, water entry pressure, media compatibility and temperature, rather than starting from a rating and working backwards.

What to specify so the rating means something

Six fields, and the first one is where most projects go wrong.

1. The IP rating of the finished assembly, with the agreed conditions written in for IPX8, and the standard the test is referenced to.
2. The airflow the enclosure needs at the pressure differential it will actually see, which is what the published 70 mbar airflow figures are there to be compared against.
3. The water entry pressure required, expressed in the pressure the membrane will meet rather than in a rating, so it can be checked against the immersion depth.
4. Media compatibility for the environment: solvents, oils, salt, cleaning agents.
5. Operating temperature for the actual enclosure, and the die-cut geometry, whether encapsulated, threaded or self-adhesive.
6. The evidence: a rating for the component, and a test on the assembled enclosure to the standard the customer requires.

When you want that answered against a specific housing rather than a datasheet, our contact page is the place to state the IP requirement, the environment and the enclosure, and get a model recommendation with the published figures behind it.

Frequently asked questions