| Physical mask thickness d (mm) | Equivalent thickness de (mm) |
Unstretched mask | 2.30 | 1.20 |
5 cm stretched mask | 2.19 | 1.15 |
10 cm stretched mask | 2.00 | 1.10 |
15 cm stretched mask | 1.90 | 1.09 |
20 cm stretched mask | 1.80 | 1.00 |