Measure equal parts A and B by volume, mix hard for about 20 to 30 seconds, then pour into a dry, contained cavity and let it rise. It foams in seconds and cures rigid and closed-cell, so it resists water and adds flotation. Work between about 75°F and 80°F for a full rise, fill deep cavities in layers, and pour only as much as you can mix in one batch.

Density is the cured weight per cubic foot, and it sets the foam's strength. Higher density means more strength but less expansion per kit:

• 2 lb: the standard for flotation and filling voids under decks and seats, the most common marine choice.
• 4 lb and 8 lb: stronger and stiffer for transoms, stringers, and structural coring.
• 16 lb: a high-strength structural and tooling foam.

Expansion depends on density, since lighter foam rises more from the same liquid. As a guide, a 2-quart kit of 2 lb foam yields roughly 2.5 cubic feet, and a 2-gallon kit yields around 10 cubic feet; higher-density foams expand less for the same kit. Because it rises fast and far, pour into a contained space and fill deep cavities in layers so it does not overflow.