Most solids and liquids have a positive coefficient of thermal expansion. That's how you can shrink-fit metal parts and put a rod in a hole that's made smaller smaller than the rod is... cool the rod and heat the part with the hole.

Heat a metal and it becomes less dense; cool it and it becomes more dense.

Water has a negative coefficient of thermal expansion as it changes from liquid to solid, and it becomes less dense. It expands under those conditions, as anyone who has exposed water pipes and an unexpected spell of arctic temperatures knows [g].

If it weren't for this somewhat unusual characteristic, there would be no icebergs floating in the oceans, as the ice would become more dense sink to the bottom.