Polyurethane bouyancy foam.
A non CFC rigid low density polyurethane foam system. Pouring Foam is a flame retarded, NON?CFC, two pack rigid polyurethane foam system producing foam with a nominal free rise density of 36?38 kg/m3. Thus a 1 litre kit will produce a free rise rigid foam bulk of about 25 litres. These are often called an expanding foam.
Often used for flotation chambers in boats. It can also be molded into odd shapes and carved easily once rigid.
It is 88% closed cell, however as it is a polyurethane, if it is constantly immersed, it will over time gain weight.