why do silicone rubber heaters contract when heated instead of expanding

Silicone rubber heaters are designed to expand when they are heated, not contract. This is because silicone rubber has a positive coefficient of thermal expansion, which means that it expands when it is heated and contracts when it cools down.

If you have observed a silicone rubber heater contracting when heated, there may be several possible reasons for this. One possible explanation is that the heater was not designed or manufactured properly, and the materials used in the construction of the heater may not be of high quality. In some cases, the heating element inside the silicone rubber band may have been damaged or improperly installed, which could cause the heater to behave unpredictably.

Another possibility is that the silicone rubber heater was subjected to extreme temperatures, which can cause it to behave abnormally. If a silicone rubber heater is heated beyond its maximum operating temperature, it can begin to break down and lose its elasticity, which could cause it to contract instead of expanding.

It's also worth noting that the exact behavior of a silicone rubber heater when heated will depend on various factors, including the specific type of silicone used, the temperature and duration of the heating process, and the configuration of the heating element. If you are experiencing problems with a silicone rubber heater, it's best to consult the manufacturer or a qualified technician for assistance.