One reference for every figure behind insulating mat selection: IEC 61111 Class 0-4 voltages and proof test levels, the thickness window for each class, the ASTM D178 ladder, colour codes and retest voltages.
This page is the reference companion to our guide on how to choose insulating mat thickness: everything here is a figure you can quote directly on a purchase order, an inspection sheet or a tender document. Figures are taken from the IEC 61111 class definitions and from published manufacturer data sheets; where a number is edition-specific we say so.
1. IEC 61111 class table: voltage and test levels
IEC 61111 sorts insulating matting into five classes. The class is the primary designation on the product marking, the data sheet and the type test report: it is what defines which installations the matting may be used on.
| Class | Max use voltage (AC) | AC proof test voltage | Withstand voltage |
|---|---|---|---|
| Class 0 | 1.0 kV | 5.0 kV | 10.0 kV |
| Class 1 | 7.5 kV | 10.0 kV | 20.0 kV |
| Class 2 | 17.0 kV | 20.0 kV | 30.0 kV |
| Class 3 | 26.5 kV | 30.0 kV | 40.0 kV |
| Class 4 | 36.0 kV | 40.0 kV | 50.0 kV |
The three voltage columns are not interchangeable. The maximum use voltage is the working limit of the installation; the proof test voltage is what the mat is tested at in the factory; the withstand voltage is the level it must survive. When someone quotes "a 20 kV mat", they are almost always referring to the proof test voltage, which belongs to Class 2 — a product with a 17 kV working limit.
A version note worth knowing: IEC 61111:2009 (second edition) is the edition still cited by most published data sheets. A third edition, IEC 61111:2026, cancels and replaces the 2009 edition. A current specification should name the edition it is written against rather than assuming that "IEC 61111" always means one fixed set of numbers.
2. Thickness table: what the standard actually sets
This is where most published charts go wrong. IEC 61111 does not assign a single thickness to a voltage class. It sets a recommended thickness and a maximum thickness permitted for each class, and any value inside that window may be supplied provided the mat passes the electrical tests for the class.
| Class | Recommended thickness | Maximum thickness permitted |
|---|---|---|
| Class 0 | 2.0 mm | 6 mm |
| Class 1 | 2.0 mm | 6 mm |
| Class 2 | 3.0 mm | 8 mm |
| Class 3 | 4.0 mm | 11 mm |
| Class 4 | 5.0 mm | 14 mm |
Read across the two tables and the relationship becomes clear: the class fixes the voltage; thickness only has to sit inside the window. This is why two fully compliant Class 3 mats can be supplied at 3 mm and at 4 mm by different manufacturers — one published Class 3 mat is offered at 3 mm, another at 4 mm. Both can pass the same class test.
A thicker mat does not have a higher voltage class. Increasing thickness inside a class improves puncture resistance, abrasion life and load bearing. It does not change the electrical rating.
The same logic explains why the widely circulated rule of thumb "5 mm = 10 kV, 10 mm = 33 kV" is not a standard. Those pairings come from marketplace listings, not from the class definitions, and they should not be written into a technical specification.
DC installations
DC ratings are published separately and are higher than the AC figures for the same class. Published examples: a 2 mm Class 0 mat listed at 1 kV AC and 1.5 kV DC; a 5 mm Class 4 mat listed at 36 kV AC and 54 kV DC. If the installation is DC, ask for the DC column specifically rather than assuming the AC figure covers it.
3. ASTM D178 ladder (North America)
Where ASTM D178 is the specified standard, the structure is familiar but the thicknesses are different, because ASTM assigns one thickness to each class.
| Class | Max use voltage | AC proof test | Dielectric test | Thickness |
|---|---|---|---|---|
| Class 0 | 1.0 kV | 5.0 kV | 10.0 kV | 3.2 mm |
| Class 1 | 7.5 kV | 10.0 kV | 20.0 kV | 4.8 mm |
| Class 2 | 17.0 kV | 20.0 kV | 30.0 kV | 6.4 mm |
| Class 3 | 26.5 kV | 30.0 kV | 40.0 kV | 9.5 mm |
| Class 4 | 36.0 kV | 40.0 kV | 50.0 kV | 12.7 mm |
The thickness ladder therefore runs from 3.2 mm to 12.7 mm. Published tolerances for ASTM matting are typically ±0.8-1.2 mm on thickness and ±13-25 mm on width, depending on class and width. Type I is the default grade; Type II properties (IIA ozone resistance, IIB flame resistance, IIC oil resistance) are specified separately or in combination.
4. Colour codes and marking
Where the colour code is applied, it identifies the live-working double-triangle symbol — it is not a substitute for reading the class designation.
| Class | Colour of the double-triangle symbol |
|---|---|
| Class 0 | Red |
| Class 1 | White |
| Class 2 | Yellow |
| Class 3 | Green |
| Class 4 | Orange |
A compliant mat is marked with the manufacturer identification, the live-working double-triangle symbol, the IEC 61111 reference, the month and year of manufacture, the category where applicable, and the class designation. In roll form these markings are repeated along the length — commonly every 400 mm, and not less than once per metre — so that a cut section still carries identification.
5. Retest voltages for matting in service
Matting that has not been used for 12 months must be visually inspected and electrically tested before it goes back into service. The test level depends on the class.
| Class | Type test voltage | Duration |
|---|---|---|
| Class 0 | Visual inspection only | - |
| Class 1 | 10 kV | 1 minute |
| Class 2 | 20 kV | 1 minute |
| Class 3 | 30 kV | 1 minute |
| Class 4 | 40 kV | 1 minute |
This is a common audit finding: matting that has been in store for a year is often assumed to be ready for use. It is not, until the inspection and test have been carried out and recorded.
6. Physical and environmental figures worth quoting
- Puncture resistance - typically published at 70 N minimum for insulating matting.
- Slip resistance - IEC 61111 requires both faces to be slip resistant; 50 N minimum is typical in published data.
- Ageing - after 168 hours at 70 ± 2 °C, puncture resistance typically must remain above 80 % of its original value.
- Low temperature - no visible tearing or cracking after exposure at −25 ± 3 °C.
- Acid and oil resistance - mechanical values typically must remain above 75 % of original.
- Operating temperature - commonly −25 °C to +55 °C, with low-temperature grades extending the cold limit to −40 °C.
- Storage - one published recommendation is +10 °C to +21 °C, away from heat sources, direct sunlight, artificial light and ozone, without compression or bending.
7. Turning the tables into a purchase order line
A specification that survives a factory acceptance test names the standard and edition, the class, the dimensions and the tolerance. A workable line reads:
Insulating matting to IEC 61111:2009, Class 3, maximum use voltage 26.5 kV AC, thickness 4 mm within the tolerance stated on the data sheet, roll 10 m x 1.0 m, fine-ribbed anti-slip surface on both faces, marked with manufacturer identification, live-working double-triangle symbol, standard reference, month and year of manufacture and class designation at intervals not exceeding 1 m, supplied with the type test report for the class.
Where an ASTM-referenced product is required instead, keep the same structure and change the thickness figure to the ASTM ladder value for that class — 9.5 mm for Class 3, for example.
For the reasoning behind the class choice itself — phase-to-phase versus phase-to-ground, environment, mechanical duty and the mistakes that fail an audit — see the insulating mat thickness selection guide.
Matting in the classes covered by these tables is supplied as the IEC 61111 high voltage insulating rubber mat, the 10 kV / 35 kV standard insulating mat and the 5 kV / 10 kV / 35 kV high protection mat.
If you are specifying matting and want the class and thickness confirmed against your network voltage, send us the installation voltage and the working conditions. We will confirm the class, the thickness window and the available roll sizes, and return the type test report for the class quoted.
Need this confirmed against your own installation?
Send us the network voltage, the standard you are specifying against and the ambient conditions. Our engineers will confirm the class, thickness and test report, and reply with lead time.
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