The weight of polyethylene film depends on its thickness and density. Typically, low-density polyethylene (LDPE) has a density of 0.91-0.93 g/cm³, and high-density polyethylene (HDPE) has a density of 0.94-0.97 g/cm³. The calculation formula is:
Weight (g/m²) = Thickness (mm) × Density (g/cm³) × 1000
For example:
- 0.01mm thick LDPE film: 0.01 × 0.92 × 1000 = 9.2 g/m²
- 0.05mm thick HDPE film: 0.05 × 0.95 × 1000 = 47.5 g/m²
Referring to the density range of polyethylene film in the national standard GB/T 4456-2008, the actual weight may fluctuate by ±5% due to additives (such as UV protectants).
Key Factors Affecting Weight
1. Thickness Difference: Agricultural films (0.03-0.1mm) are heavier than packaging films (0.01-0.03mm).
2. Material Type: Linear low-density polyethylene (LLDPE) has a slightly higher density than LDPE, resulting in a 3%-8% increase in weight for the same thickness.
3. Manufacturing Process: Blow molding may produce uneven thickness, leading to localized weight fluctuations.
How to Choose the Appropriate Weight for Your Needs?
- Supermarket Plastic Bags: Commonly used is 0.015mm LDPE, approximately 14 g/m², which must comply with the environmental standard GB/T 21661-2020.
- Greenhouse Film: 0.08mm HDPE is recommended, approximately 76 g/m², offering higher tensile strength.
Professional Data and Common Misconceptions
1. Some manufacturers' "grammage" label may include the printing layer; the actual substrate weight should be reduced by 2-3 g/m².
2. The international standard ISO 4591 stipulates that thickness measurement should be performed using a micrometer to obtain the average value of 10 points to avoid errors.