Polypropylene is non-toxic, odorless, tasbess, milky white, high-crystallized polymer, density is only 0. 90——0. 91g/cm3, which is one of the lightest varieties of all plastics. It is particularly stable in water; the water absorption is onlythe molecular weight is about 80 to 150 thousand. The bability is good, but the shrinkage rate is large (1%~2.5%). The thick walled products are easy to sag, and some parts with higher dimensional accuracy are difficult to meet the requirements, and the product’s surface gloss is good.