Table 1 N category mass per unit area, thickness Thickness specifications/mm1.21.52.0 Upper surface materials PE, PET, DPE, PET, DPE, PET, D Mass per unit area/(kg/m2) ≥1.21.52.0 Thickness/mm Average ≥1.21.52.0 Minimum single value 1.01.31.7 Table 2 PY class mass per unit area, thickness thickness specification/mm2.03.04.0 Upper surface material PE, DSPE, DSPE, DS mass per unit area/(kg/m2) ≥2.12.23.13. 24.14.2 Thickness/mm average value ≥2.03.04.0 minimum single value 1.82.73.7