If you are looking for an insulation film with UL 94 V-0 in 0.125 or 0.25 mm, you will often find the rating VTM-0 in data sheets. VTM-0 is not a weaker V-0. It is the result of a separate test method that UL developed for thin films. The reason: in the V test, thin films deform so much that the result would be meaningless. The VTM method is intended to provide a statement for these films that is comparable to V-0. VTM-0 is the best class of this method. Comparable does not mean identical, however: if a specification literally requires V-0, VTM-0 is not an automatic substitute.
What is UL 94?
UL 94 is the standard of the testing organisation UL (Underwriters Laboratories) for the flammability of plastic materials in devices and appliances. For electrical insulation, the core is the V test with classes V-0, V-1 and V-2, V-0 being the best. For thin films that are not suitable for the V test, there is the VTM method with classes VTM-0, VTM-1 and VTM-2. UL 94 also includes the horizontal burning test HB and the test with a larger flame (5VA, 5VB).
The international equivalent of the V test is IEC 60695-11-10; that of the VTM test is ISO 9773.
A UL 94 rating always applies to the tested material in the tested thickness and colour. The same material can therefore achieve VTM-0 at 0.25 mm and V-0 at 0.43 mm.
How the tests work
The V test (V-0, V-1, V-2)
A specimen bar 125 mm long and 13 mm wide is clamped at the top and hangs vertically. A layer of cotton is placed underneath. A 20 mm high flame is applied to the lower end from below for ten seconds and then removed. The time the bar continues to burn is measured. As soon as it goes out, a second ten-second flame application follows. Five bars are tested.
For V-0, each bar must self-extinguish within 10 seconds after each flame application. The total afterflame time of all five bars must not exceed 50 seconds. No flaming drips that ignite the cotton are allowed, and no bar may burn up to the clamp. V-1 allows 30 seconds of afterflame time per bar. V-2 corresponds to V-1 but allows flaming drips that ignite the cotton.
Why thin films are tested differently
A thin film does not behave like a bar in a flame. It shrinks away, curls up or bends away from the flame. The V test would then no longer measure how well the material resists fire, but how quickly it deforms. This is why the VTM method was developed for thin materials. VTM stands for "Vertical Thin Material".
So if a film is tested to VTM rather than V, this is not a sign of poorer fire protection. It is the test intended for this form of material.
The VTM test (VTM-0, VTM-1, VTM-2)
A film strip 200 mm long and 50 mm wide is rolled into a tube around a mandrel with a diameter of 12.7 mm and secured at the upper end with tape. The mandrel is then withdrawn. A mark is made 125 mm from the lower end. The tube hangs vertically above a layer of cotton and is exposed twice to a 20 mm high flame for three seconds each time. Five specimens are tested.
For VTM-0, each specimen must extinguish within 10 seconds after each flame application. The total afterflame time of all five specimens must not exceed 50 seconds. No specimen may burn up to the 125 mm mark, and no flaming drips may ignite the cotton. VTM-1 and VTM-2 are graded like V-1 and V-2.
V-0 and VTM-0 compared
| V-0 | VTM-0 | |
|---|---|---|
| For which material | bars, sheets, thicker films | thin films that deform in the V test |
| Specimen | bar 125 × 13 mm, vertical | film 200 × 50 mm, rolled into a tube, vertical |
| Flame application | twice 10 seconds | twice 3 seconds |
| Afterflame time per specimen | max. 10 seconds | max. 10 seconds |
| Afterflame time, five specimens total | max. 50 seconds | max. 50 seconds |
| Flaming drips igniting the cotton | not allowed | not allowed |
| Rank | best class of the V test | best class of the VTM test |
The extinguishing limits are the same. What differs is the shape of the specimen and the duration of the flame application. The VTM method therefore provides a statement for thin films that is comparable to V-0, but not an identical test result.
What this means for your choice of material
What matters is what your product standard or your customer's specification requires.
- The specification says "V-0 or VTM-0". Then a thin film rated VTM-0 meets the requirement.
- The specification says only "V-0". Then you need a material that achieves V-0 at your installed thickness. For thin films, this usually means choosing a greater thickness.
- You are not sure. Ask your test laboratory or the body that approves your device before you fix the thickness. A later change costs more than a question.
Also always check three details together: flammability rating, thickness and colour. A rating only applies to the combination listed with UL.
DURAVOLTA flammability ratings by thickness
DURAVOLTA is the halogen-free, flame-retardant polypropylene film from 1A STAR technische Kunststoffe GmbH in Kirchhundem, Germany, listed with UL under File number E354767.
| DURAVOLTA type | Thickness | UL 94 |
|---|---|---|
| DURAVOLTA 10 | 0.10 mm | not UL rated |
| DURAVOLTA 12 | 0.125 mm | VTM-0 (in-house test, UL listing in preparation) |
| DURAVOLTA 25 | 0.25 mm | VTM-0 |
| DURAVOLTA 43 | 0.43 mm | V-0 |
| DURAVOLTA 76 | 0.76 mm | V-0 |
| DURAVOLTA 100 | 1.00 mm | V-0 |
The rating applies to the standard white version. Sheets with a thickness of 2 and 3 mm are not UL rated; experience shows that the thicker a material is, the more easily it meets fire requirements.
If your specification requires V-0, DURAVOLTA 43 at 0.43 mm is the thinnest suitable thickness. If VTM-0 is sufficient, it is DURAVOLTA 25 at 0.25 mm.
All UL values, production details and the product range are on the page DURAVOLTA: manufactured by 1A STAR in Kirchhundem, Germany.
Frequently asked questions
Is VTM-0 worse than V-0?
No. VTM-0 is the best class of the VTM test, just as V-0 is the best class of the V test. The VTM method was developed to obtain a statement comparable to V-0 for thin films, and the extinguishing limits are the same. Because the specimen shape and flame duration differ, however, the two classes are not interchangeable if a specification explicitly requires V-0.
Why does a 0.25 mm film not have V-0?
Because thin films are usually tested with the VTM method. In the V test they shrink or deform, and the result would be meaningless. The VTM test rolls the film into a tube and is therefore tailored to this form of material.
Can I use VTM-0 if V-0 is required?
That depends on the wording of the requirement. If it says "V-0 or VTM-0", yes. If it says only "V-0", you need a material with V-0 at your installed thickness. If in doubt, clarify this with your test laboratory before you fix the thickness.
Does V-0 apply to all thicknesses of a material?
No. A UL 94 rating applies to the tested thickness or the listed thickness range and the tested colour. DURAVOLTA, for example, achieves V-0 from 0.43 to 1.1 mm and VTM-0 at 0.25 mm; DURAVOLTA 12 at 0.125 mm achieves VTM-0 by in-house testing, and the UL listing is in preparation.
Which international standard corresponds to UL 94?
The V test corresponds to IEC 60695-11-10, the VTM test to ISO 9773. According to the UL listing, the DURAVOLTA flammability ratings are also confirmed according to IEC 60695-11-10.
As of: October 2026