Expanding urethane pour foam is a two-part, closed-cell liquid foam system that expands rapidly when mixed. It's used for flotation, insulation, soundproofing, and filling voids in boat hulls, decks, and other marine structures.

No. This is pour-in-place foam, not spray foam. You mix the two parts, pour the liquid into the cavity, and it expands to fill and harden. Spray foam uses different chemistry and equipment. For flotation, coring, and filling voids, pour foam is the right product: just pour in lifts and let each rise before adding more.

Foam expansion is temperature-sensitive. For best results, both the foam and the working environment should be around 80°F. At 50°F, expansion can be reduced by 50% or more. Warm the product before use if needed.

Use 2 lb foam for standard flotation applications. It offers about 60 lbs of buoyancy per cubic foot. For added strength or to support a deck, 4 lb foam is a better option.

Once Parts A and B are mixed, you’ll have roughly 45 seconds before expansion begins. Stir vigorously for about 25 seconds, then pour immediately. The foam expands fully in about 5 minutes and hardens in 15 minutes.

Yes. You can pour in multiple layers, waiting 15–20 minutes between pours. This method helps control expansion and ensures complete curing without overheating.

Measure the volume of the space in cubic feet (length × width × height). Each cubic foot requires about 2 quarts of liquid foam (combined Part A and B).

Yes. Once cured, urethane foam is resistant to gasoline, acetone, and most solvents. It cannot be dissolved—only mechanically removed by sanding or scraping.

Yes, you can pour foam into molds. For easy release, use a mold release wax like Partall #2 or line the mold with smooth plastic sheeting. Porous molds should be sealed before applying wax.

Yes, with care. Calculate the internal volume, and make sure the cavity is dry and sealed. The foam only flows a few feet before it expands, so for long, narrow spaces, over 5 feet long or under 2 inches across, results vary and you should test first. See our full guide on filling pontoons with foam.

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.