This engineering lesson has students designing and building a raft using what they know about density and buoyancy. Students have the opportunity to show creativity while working within constraints in cooperative groups. Groups of students must decide what materials would be good to use based on the density of the material. The boat must be shaped so it will support added weight without tipping over. You can increase the difficulty by having students calculate the density of each boat and compare it to the amount of weight each boat could hold.