Eli5: Materials expand when heated and contracts when cooled. So why does water expand when it freezes instead of contracting?

Question

Eli5: Materials expand when heated and contracts when cooled. So why does water expand when it freezes instead of contracting?

In: 24

Answer 1

There are other materials that do the same. Not many but some. The one that surprised me the most when I had to deal with it was a carbon fiber we were using as a retention sleeve for a very high speed rotor. It would be pressed onto the rotor and for that we had to cool it so it would expand.