What is the hot water bottle shell plastic usually made of, PP, PC or other?

Currently on the market to sell the warmer skin all PP (polypropylene) production, the reason is that polypropylene has a better impact resistance and toughness, and in the case of impact by hot water will not be deformed, virtually immune to chemicals, hardness is not too high, so as to have better protection to put down the warmer is the time when the vibration generated.

PC (polycarbonate) hardness is very high, but in the case of very low thickness will be broken like glass, high transparency, not easy to process, prone to bubbles, and the nature of ABS is similar. Currently on the market plastic glass is basically PC material.