Soy Insulation – Too Good to Be True?

Soy-based spray foam insulation uses soy oil to replace some of the propellant used in conventional spray foam. The manufacturers claim the product is more environmentally friendly.

Soybean Foam Insulation Components

Soybean Foam Insulation

All spray foam insulation is a mix of isocyanurate (the hardening agent) and polyol (a resin). Approximately 50/50. The soy-based product continues to use 50% isocyanurate but replaces some of the polyol ingredients with soy oil. Polyol needs to be stable to produce an acceptable finished product. Any added soy oil tends to make it less stable. Five percent seems to be the maximum amount that can be used.

The average soy oil content in the polyol seems to be about 5%. Meaning that the soy content of the total product is 2 ½%. Some manufacturers claim 15% soy oil. That is still only a total of 7 ½% of total volume.

The soy oil replaces another plant-based renewable ingredient–sugar. Meaning that the product might not be any more environmentally friendly but less stable.

Are Soy-Based Insulation Claims Greenwashing?

They appear to be. The Federal Trade Commission (FTC) is investigating some of the companies’ claims of “soy-based spray foam insulation.” Soy-based implies much more soy oil in the product than 2 ½%. Many–if not most–of the manufacturers list the amount of soy in their products as a “Trade Secret.”

Reasons To Buy Soy-Based Foam Insulation

Like all spray foam insulations, soy foam insulation sprayed on interior walls and roofs provides an R-value of up to R-6.5. It seals gaps and cracks. It eliminates voids behind electrical wires and boxes, plumbing, and ductwork.

Soy-based foam eliminates air leaks and is insect and rodent-resistant. It is moisture resistant so does not require a vapor barrier if installed two inches thick or more. It also does not contain formaldehyde, urea, fire retardant, or hydrofluorocarbons.

Soy insulation is available in both open cell and closed cell formulations. Open cell foam has a lower R-value. It expands up to 100 times its original size and needs to be cut off and disposed of. Closed cell foam has a higher R-value. It does not expand as much.

Both products have the same characteristics as other spray foams.

Reasons Not To Buy Soy-Based Foam Insulation

Besides the greenwashing and questionable claims, there are a few other reasons not to have soy-based foam insulation installed.

  • Cost. More expensive than regular polyurethane spray foam insulation.
  • Inconsistency. Does not spray consistently; therefore thickness and coverage can be spotty.
  • Density. Spray may be less dense in spots which means lower R-values.
  • DIY. Not available in DIY kits.
  • Shrinks. There have been some reports of the product shrinking after it cures.

Inconsistent insulation increases heating and cooling costs and reduces home comfort. The best spray foam option may be to use one of the proven products installed by a reputable company. At least until soy-based insulation manufacturers have solved the problems.