Considering from two aspects of packaging cost and performance requirements, the thickness selection of each layer of composite flexible packaging materials should be carefully weighed. In general, the heat seal layer can be determined by market generalization and standardization, the strength support layer is generally determined according to the weight of the packaged product, and the thickness of the functional material is generally determined by the shelf life of the product.

1.Permeability coefficient: 

According to the maximum allowable water absorption of the packaged product or the maximum allowable water removal of the product, the method is mainly suitable for the design of moisture-proof packaging products, and the key is to calculate the moisture permeability coefficient of flexible packaging composite materials.

2.Oxygen permeability coefficient:

According to the maximum allowable oxygen absorption of the packaged product, the method is mainly suitable for the product barrier packaging which is very sensitive to oxygen, and the key is to calculate the oxygen permeability coefficient of the flexible packaging composite material.

3.Number of microorganisms: 

According to the maximum allowable number of microorganisms per unit volume or unit surface area, the method is mainly suitable for mildew resistant packaging of products that are very sensitive to microorganisms, and the key is to determine the type of microbial products and the law of reproduction and growth.

4.oxygen coefficient and carbon dioxide coefficient: