Product raw material particle is different, die gap is also different. It also affects the draft ratio of the product.
The relationship between draft ratio and die clearance can be expressed by the following formula: b= T /BUR×δ, where B is draft ratio, T is die clearance, BUR is blowing ratio, and δ is film thickness.
Die gap selection, LDPE resin choose a narrow die gap, HDPE very thin film should be adopted to widen the die gap.
Die clearance of commonly used resins is shown in the table.
| Film | PVC | LDPE | HDPE | LLDPE | PP | PA |
| Die Clearance mm | 0.8-1.2 | 0.5-1.0 | 1.2-1.5 | 1.5-2.5 | 0.7-1.0 |
0.5-0.75 |