ASTM C1136 facing types classify flexible vapor retarders for thermal insulation into ten classes, Type I through Type X, by water vapor permeance, burst strength and tensile strength. Most foil-based facings used on duct wrap, metal building insulation and pipe work are specified to Type II, which caps permeance at 0.02 perm and requires a minimum 35 psi burst strength and 30 lb/in machine-direction tensile. The type number is a performance class, not a product name, so two facings described the same way can land in different types. Match the datasheet values to the type, then confirm the test method and the edition of the standard before you sign the order.
Quick answer: which ASTM C1136 type do you need?
- Below-ambient service (chilled water, cold duct, refrigeration) needs 0.02 perm or lower, which points to Type I or Type II.
- Ambient building work, including metal building wall and roof assemblies, accepts 0.10 perm, so Type III or Type IV is enough and usually costs less.
- Type I and Type III carry the higher strength set (55 psi burst, 45 lb/in machine-direction tensile); Type II and Type IV carry the lower one. Pick by handling abuse, not by habit.
- Types VII through X are film-based retarders for pipe, tank and equipment work where near-zero permeance matters more than tensile strength.
- Above 150 °F (66 °C) surface temperature, ASTM C1136 no longer applies at all, and the facing has to be qualified on temperature instead.
- Outdoors, no C1136 facing is a weather barrier. The facing stays, and a jacket goes over it.
What ASTM C1136 actually covers
ASTM C1136 is the Standard Specification for Flexible, Low Permeance Vapor Retarders for Thermal Insulation. It covers flexible sheet materials with a water vapor permeance of 0.15 perm (8.63 ng/Pa·s·m²) or lower and surface burning characteristics of 25 flame spread / 50 smoke or lower when tested to ASTM E84. The current edition states the materials are intended for surface temperatures between -20 and 150 °F (-29 to 66 °C).
That scope is narrower than most buyers assume. Three things sit outside it, and each one causes real claims.
| In scope | Out of scope |
|---|---|
| Flexible laminated facings (FSK, ASJ, PSK, MSK) supplied in roll form | Mastics and coatings applied in liquid form |
| Film-based retarders on pipe, tank and equipment | Weather barriers and exterior cladding |
| Permeance up to 0.15 perm, tested to ASTM E96 | Surface temperatures above 150 °F (66 °C) or below -20 °F (-29 °C) |
| The facing as a flat sheet, tested free of joints | The sealed system: seams, laps and penetrations |
The last row deserves its own paragraph. Permeance is measured on a flat sheet with no joints present. The ASHRAE Handbook, Chapter 23, makes the point directly: the permeance of the material is not the permeance of the installation, because joints, laps and tape dominate the real performance. ASTM C1809, first published in 2015, exists to prepare sealed joints for permeance testing with ASTM E96, precisely because the industry had no repeatable way to test the thing that actually fails. If your specification says “0.02 perm” and says nothing about how the seams are sealed, you have specified the least important 0.02 perm on the job.
The ten types at a glance
Table 1 of the standard sets minimum physical properties for each type. The values below follow the C1136-23 edition.
| Type | Permeance, max, perm | Burst, min, psi | Tensile MD, min, lb/in | Tensile CD, min, lb/in | Dimensional change, max, % |
|---|---|---|---|---|---|
| I | 0.02 | 55 | 45 | 30 | 0.50 |
| II | 0.02 | 35 | 30 | 20 | 0.50 |
| III | 0.10 | 55 | 45 | 30 | 0.50 |
| IV | 0.10 | 35 | 30 | 20 | 0.50 |
| V | 0.15 | 55 | 45 | 30 | 0.50 |
| VI | 0.15 | 35 | 30 | 20 | 0.50 |
| VII | 0.01 | 70 | 11 | 10 | 1.0 |
| VIII | 0.02 | 60 | 8 | 7 | 1.0 |
| IX | 0.00 | 80 | 25 | 25 | 0.5 |
| X | 0.01 | 75 | 60 | 50 | 0.5 |
Permeance in metric units: 0.02 perm equals 1.15 ng/Pa·s·m², 0.10 perm equals 5.75, 0.15 perm equals 8.63. Types VII through X also carry a surface water resistance limit of 2.0 g/m².
Two cautions before you copy that table into a specification.
First, the type definitions have changed between editions. In the C1136-09 edition, Type V meant 0.02 perm with a 100 psi burst requirement, and the standard listed only Types I through VIII. The 1995 edition expressed puncture resistance in Beach units instead of burst strength. A master specification written in 2010 that calls for “Type V” is not asking for what C1136-23 calls Type V. When you inherit an old spec, ask which edition it was written against, or restate the properties explicitly.
Second, these are minimums, not typicals. A facing can meet Type II and still tear in the field if your handling is rougher than the test assumes. The type number is a floor, and volume buyers usually order above it.
How the types map to real facings
The facing families you actually buy line up against the types like this. Values marked “typical” are industry-typical, not a guarantee for any specific mill run; every one of them has to be confirmed on the datasheet.
| Facing family | Structure | Typical type | Where it wins | Watch out for |
|---|---|---|---|---|
| FSK | Aluminum foil, fiberglass scrim, kraft paper | Type II, Type I in heavier builds | Duct wrap, metal building liner, general vapor control | Foil is 6 to 9 micron on lighter builds; kraft loses strength when damp |
| ASJ | White kraft or polymer face, scrim, foil or film backing | Type II | Pipe insulation and exposed indoor work where appearance matters | Not for outdoor use without a jacket; surface stains show |
| PSK | Polypropylene film, scrim, kraft | Type II | Exposed duct where a cleanable white surface is wanted | Adhesive system decides the fire classification, so check the E84 report |
| MSK | Metallized polyester film, scrim, kraft | Type II when built for it | Cost-sensitive metal building and duct work | Metallized film is thinner than foil; puncture resistance is lower |
| FSM (foil scrim MPET) | Foil, scrim, MPET film | Type II | Duct wrap where a fully closed vapor face is needed | Check the temperature rating of the adhesive, not just the foil |
| Foil kraft (FK) | Foil and kraft, no scrim | Often below the C1136 strength floor | Light-duty facing where vapor control is the only job | Tensile usually fails Type II minimums; confirm before specifying |
| Double foil (DS type) | Foil both sides, scrim and kraft core | Type I or II | Reflective assemblies and premium duct work | Needs an adjacent air space to deliver any reflective benefit |
| Foil fiberglass cloth | Foil on woven cloth | Above the C1136 floor | Industrial equipment, high-abuse, higher temperature | Heavier and stiffer to wrap; costs more per square meter |
The pattern worth internalizing: the type ladder sorts by permeance and strength, and the facing family sorts by surface and construction. An FSK facing and a PSK facing both land in Type II routinely, because the foil and the polypropylene film both block vapor. What separates them is appearance, cleanability and how each one ages, none of which the type number tells you.
Reading a datasheet against the standard
Every property in Table 1 ties to a specific test method, and the method matters as much as the number. Two labs can report “0.02 perm” and disagree if one used the desiccant method and the other used the wet-cup method.
| Property | Test method | What to check |
|---|---|---|
| Water vapor permeance | ASTM E96, desiccant method per C1136 | Which procedure was used, and whether the sample was flat sheet or a sealed joint to ASTM C1809 |
| Surface burning | ASTM E84 | Flame spread 25 / smoke developed 50, on the facing itself, not the insulation |
| Tensile, paper-based facings | ASTM D828 | Specimen 2 in (51 mm) wide, 1 in (25 mm) between jaws; MD and CD reported separately |
| Tensile, plastic film facings | ASTM D882 | Same layout; do not accept one direction only |
| Dimensional change | ASTM D1204 | 15 minutes at 200 °F (93 °C); limit 0.5 % for most types |
| Fungi resistance | ASTM C1338 | Three specimens; growth on any one is a fail |
| Thermal integrity | ASTM C1263 | How the laminate holds together at temperature |
| Elevated temperature and humidity | ASTM C1258 | The test most buyers never ask for and most need |
If a supplier sends a datasheet with permeance and tensile but no test methods and no edition reference, the datasheet is marketing, not evidence. Ask for the report number. A supplier who has actually tested the product produces it in a day; one who has not will go quiet.
The temperature ceiling that buyers miss
The scope limit of -20 to 150 °F (-29 to 66 °C) is the single most overlooked line in the standard. It exists because the aluminum foil will happily go far hotter, but the adhesive holding the laminate together will not.
Hot water piping, steam condensate, kitchen exhaust and any equipment near a heat source all run past 150 °F at the insulation surface. On those jobs the C1136 type number tells you nothing, and specifying “Type II FSK” gives a false sense of coverage. What governs is the continuous service temperature of the adhesive system, checked through ASTM C1258 and C1263 results, plus the substrate’s own limit. Glass wool substrates commonly carry a 250 °F (121 °C) limit when faced, lower than the unfaced product, and the facing is the reason.
The failure mode when this is ignored is delamination: the adhesive softens, the foil separates from the scrim, and the vapor retarder becomes loose foil flapping over wet insulation. We have seen it on retrofit jobs where a standard duct-wrap facing was reused on a hot water line because “it is the same silver stuff.” It is not.
Where facings actually fail on site
Laboratory values are the easy part. These are the failure modes that generate the phone calls.
- Unsealed seams. The sheet tests at 0.02 perm and the job leaks anyway, because laps were stapled and never taped. Seal every longitudinal seam and butt joint with a tape rated for the service temperature, and staple no more than 6 in (150 mm) apart under the tape.
- Foil corrosion in wet, alkaline or chloride-laden environments. Aluminum foil and fresh concrete, cementitious fireproofing or marine air do not get along. Pitting starts within months and the vapor face is gone in a year or two. Where the environment is aggressive, move to a polymer-faced or laminated-film retarder and protect the foil.
- Cold-crack. Some vinyl and low-grade film facings crack at low temperature when flexed. It shows up on winter installations when the roll is unrolled in freezing weather and the facing splits along the fold. Check the low-temperature rating before scheduling a winter install.
- The double-retarder trap. A faced blanket inside a wrapped building film gives two vapor retarders with a cavity between them. Moisture that gets into that cavity has no way out. Use one retarder, in the right place, or design the assembly deliberately.
- UV exposure. Kraft and polypropylene films degrade in sunlight within weeks. Foil itself survives, but the adhesive under it may not. Anything outdoors gets a jacket, no exceptions.
- Puncture and handling damage. Hanger pins, foot traffic and sharp tools put holes in facings that no burst test predicted. The perm rating of the damaged area is effectively infinite, so heavy-traffic areas need a protective layer regardless of what the facing is.
- Adhesive failure at temperature. Covered above, and worth repeating because it is the one that voids warranties.
What to write into the purchase order
A facing order that just says “FSK facing, Type II” leaves every important decision to the cheapest bidder. Put these lines in instead.
- Full structure: foil or film gauge in microns, scrim count (4×4, 5×5, 6×6), kraft weight in g/m², adhesive type.
- ASTM C1136 type, the edition of the standard, and the test methods used, especially the E96 procedure behind the permeance claim.
- Burst strength and tensile in both directions, with the actual measured values, not just “meets Type II”.
- Surface burning characteristics to ASTM E84, 25/50, with the report number.
- Roll width, length, core diameter and slit tolerance, matched to your lamination line.
- Edge flap width if you staple-and-tape, or heat-seal edge if you run a heat-seal lamination line, which changes the facing construction entirely.
- Printing requirements, including any UL markings that must survive on the exposed face.
- Packaging: moisture-barrier wrapped rolls, end protectors, and container loading plan if it is shipping.
- A retained sample from the production run, plus a certificate of analysis referencing the order number.
If you laminate the facing onto your own glass wool or rock wool line, add one more line: confirm the facing works with your adhesive, line speed and lamination temperature before committing to a full container. The heat-seal vs adhesive lamination decision affects the facing construction, not just the process, and it is much cheaper to test on a sample roll than to discover on 20,000 square meters.
FAQ
How many types does ASTM C1136 have?
The current edition defines ten types, Type I through Type X, grouped by maximum water vapor permeance (0.00 to 0.15 perm) and minimum burst and tensile strength. Earlier editions listed fewer types with different definitions, which is why an old specification citing a type number should be checked against the edition it was written for.
Is an FSK facing automatically ASTM C1136 Type II?
No. Type II is a performance class the facing either meets or does not. Most well-built FSK facings meet it, because a continuous aluminum foil layer blocks vapor far below the 0.02 perm limit and a scrim-reinforced laminate carries the required 35 psi burst and 30 lb/in tensile. But a light-duty foil kraft facing with no scrim can share the same description and fail the strength minimums. Ask for the test report, not the acronym.
What is the difference between ASTM C1136 Type I and Type II?
Permeance is identical at 0.02 perm maximum. The difference is strength: Type I requires 55 psi burst and 45 lb/in machine-direction tensile, against 35 psi and 30 lb/in for Type II. Type I is the heavier-duty choice for work that takes handling abuse; Type II is the standard choice for duct wrap and metal building insulation where the facing is protected after installation.
What perm rating do I need for chilled water piping?
Keep it at or below 0.02 perm, which means Type I or Type II, and treat the seams as part of the rating. Cold surfaces sit below the dew point for most of the year, so any vapor path condenses inside the insulation. NAIMA recommends 0.10 perm or lower for metal building work, but below-ambient mechanical work is held to the tighter 0.02 perm figure in common practice and in ASTM C1136 Type II.
Does ASTM C1136 cover fire performance?
It sets a surface burning requirement of 25 flame spread / 50 smoke developed when tested to ASTM E84, and that is all it does for fire. It is not a reaction-to-fire classification in the EN 13501 sense, and it does not carry through to the finished laminate automatically. If the job needs a fire rating on the faced product, ask for the E84 report on that exact facing and adhesive combination.
Can I use an ASTM C1136 facing outdoors?
Not on its own. The standard covers vapor retarders, not weather barriers, and kraft and polypropylene surfaces degrade under UV. Keep the facing as the vapor control layer and cover it with aluminum jacketing, PVC or a laminate jacket designed for weather exposure. That outer jacket then carries the mechanical abuse as well.
What changed between the older and current editions of ASTM C1136?
Three things worth knowing: the type list grew from four, to eight, to ten types; Type V and Type VI were redefined (Type V moved from 0.02 perm with a 100 psi burst requirement to 0.15 perm with 55 psi); and the puncture resistance requirement in Beach units used in early editions was replaced by burst strength. Old master specifications should be restated in property terms, not by type number alone.
Next step
If you are specifying a facing for a new project or qualifying a supplier, send us the service conditions (temperature, humidity, substrate and installation method) rather than just the type number, and we will recommend a construction that meets it with margin. Request a specification or sample through the contact page and we will come back with datasheets, test reports and roll options matched to your line: Contact Donfoil.
