Multi layers - In mold foam process
Multi layers of material can be added using drop boxes during the oven cycle. An outer skin forms in the mold and a drop box holds the second layer's material that will be released after the outer skin forms.
The purpose of the inner layer(s) is to provide maximum structural instigate, provide additional insulation, add buoyancy, and dramatically decrease fuel permeation.
Second layer foam rotational molded from a in cycle drop box