I forgot the laws of physics

I used the mailman vest yesterday when delivering mail in the snow. It is like a BabyBjörn but instead of a kid you have bundles of mail on your chest. The bundles are held together by rubber bands which I take off and put on the stiff plastic back of the vest when I start on a new bundle. As I said, yesterday it was snowing, and when I came back to the office most of me was soaked and hence I put most of my clothes in the drying cabinet, put said cabinet on 70°C and then went and had lunch. This is where the laws of physics come in. Most materials expand when they get hot, but some does quite the opposite. Rubber is one example. When rubber gets hot, the carbon chains that it is made of start to vibrate more vigorously and when they do they contract. As you have guessed by now, the rubber bands that I had put on the vest got quite a bit smaller in the heat and totally warped the stiff plastic back... So, there you have it, proof that knowledge of physics can be useful even for a mailman, sort of.