Most substances expand when they are heated. Water has the unique property of expanding when it loses heat and turns into ice. If you want to check this out , fill a small plastic container to the brim with water, and put a lid on as tightly as possible without spilling any water. Put the container into the freezer. Put each can of pop into a ziploc bag and place into the freezer for two or three days. The needed materials follow.
Why Does Water Expand as It Freezes?http://edie.cprost.sfu.ca/~rhlogan/water_ex.html
The reason water expands when its temperature cools below 4 degrees Celsius is due to hydrogen bonding. Hydrogen bonding forms a weak bond between hydrogen atoms and oxygen atoms of adjacent water molecules as illustrated below. Once the temperature drops to 4 degrees Celsius, the molecules have less kinetic energy and are closer together. This allows hydrogen bonding to take place. The hydrogen bonding pulls the molecules into an open crystalline structure that occuppies more space than liquid water.
Amery, Heather The Know How Book of Experiments, Tulsa: EDC PUBLISHING(1989)p.25http://www.madsci.org/posts/archives/dec98/913733647.Ph.r.html