Imploding can

Today we did an experiment which made a can implode - exciting! We put a small amount of water in the bottom of a can and boiled it for 30 seconds. We then tipped the can upside down into a bowl of icy cold water and it imploded. We had lots of discussion around why this happened. The air in the can expanded as it heated up and when we put it in the cold water it rapidly cooled down the air which contracted and pulled the can in with it. I wonder what would happen with a tin can or a can made out of  titanium?

We also observed how warm air expands by putting a bottle with a balloon over the top in hot water. The balloon blew up as the air in the bottle got warm.