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處于自然卷曲狀態，受熱一般不會發生收縮。塑料自封袋的情況不同，主要經歷了兩個階段。原料熔化后，在指定溫度下，在外力的作用下拉伸薄膜，大分子不互相滑動，不自然的狀態凍結。

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.

室溫下塑料大分子的活動力不好，分子運動無法消除這種不自然的狀態，這就是為什么塑料自封袋在室溫下不收縮的原因。但是這只是表面現象，看起來穩定的塑料自封袋內部已經隱藏著不穩定的因素。再加熱到一定溫度后，凍結的大分子又開始活動，努力從不自然的狀態恢復到自然狀態，就會發生收縮。

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.

塑料自封袋廣泛用于各類快餐食品類、流產類、飲料類、干食品類、土特產類、礦泉水類、罐頭類等產品包裝，是熱封包裝中常用的熱收縮材料，通過吹風機，透明度高的熱收縮膜可以緊貼物品表面，提高產品等級，防止灰塵和濕氣，創造新的完美包裝效果。

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.