The shrinkage of plastic self sealing bag caused by heating is a physical phenomenon, which needs to be explained by certain physical knowledge. In short, the thermal movement of molecules leads to the shrinkage of plastic self sealing bag.

普通塑料薄膜的大分子处于自然卷曲状态，受热一般不会发生收缩。塑料自封袋的情况不同，主要经历了两个阶段。原料熔化后，在指定温度下，在外力的作用下拉伸薄膜，大分子不互相滑动，不自然的状态冻结。

The macromolecules of ordinary plastic film are in the natural curling state, and will not shrink when heated. The situation of plastic self sealing bag is different, and it mainly goes through two stages. After the raw material is melted, the film is stretched under the action of external force at the specified temperature, the macromolecules do not slide each other, and the unnatural state freezes.

室温下塑料大分子的活动力不好，分子运动无法这种不自然的状态，这就是为什么塑料自封袋在室温下不收缩的原因。但是这只是表面现象，看起来稳定的塑料自封袋内部已经隐藏着不稳定的因素。再加热到一定温度后，冻结的大分子又开始活动，努力从不自然的状态恢复到自然状态，就会发生收缩。

At room temperature, the activity of plastic macromolecules is not good, and molecular motion can not eliminate this unnatural state, which is why the plastic self sealing bag does not shrink at room temperature. But this is only a superficial phenomenon, it seems that the internal stability of the plastic self sealing bag has hidden unstable factors. After reheating to a certain temperature, the frozen macromolecules begin to move again, trying to recover from the unnatural state to the natural state, and then they will contract.

塑料自封袋广泛用于各类快餐食品类、流产类、饮料类、干食品类、土特产类、矿泉水类、罐头类等产品包装，是热封包装中常用的热收缩材料，通过吹风机，透明度高的热收缩膜可以紧贴物品表面，提高产品等级，防止灰尘和湿气，创造新的包装效果。

Plastic self sealing bag is widely used in all kinds of fast food, abortion, beverage, dry food, local specialty, mineral water, canned food and other product packaging. It is a common heat shrinkable material in heat sealing packaging. Through the hair dryer, the transparent heat shrinkable film can cling to the surface of the goods, improve the product grade, prevent dust and moisture, and create a new perfect packaging effect.