Great Stuff PestBlock and regular Great Stuff (Gaps & Cracks) are both expanding polyurethane foam sealants, but PestBlock contains a bitter chemical additive designed to discourage rodents and insects from chewing through it. The regular version has no pest-deterrent properties. Beyond that key difference, the two products also differ in color, chemical composition, and price, though they share the same basic foam technology and application method.
What Makes PestBlock Different
PestBlock’s safety data sheet reveals two chemical compounds not found in standard Great Stuff formulas: chloroalkanes and a chlorinated phosphate compound. Each makes up roughly 5 to 10 percent of the product by weight. These additives serve as both flame retardants and bitter-tasting deterrents. When a rodent or insect begins gnawing into the cured foam, these compounds create an unpleasant taste that discourages further chewing.
The other obvious difference is color. PestBlock cures to a grey foam, which DuPont says is for “easy identification” so you can visually confirm which gaps have been treated with the pest formula versus standard foam. Regular Gaps & Cracks cures to a yellowish or amber color typical of polyurethane foam.
How Well Does Each One Stop Pests
Here’s the reality: no expanding foam is completely rodent-proof. Mice and rats have teeth that can gnaw through wood, soft metals, and certainly cured polyurethane foam. PestBlock doesn’t create an impenetrable physical barrier. What it does is make the experience unpleasant enough that most rodents move on to an easier entry point. The bitter compounds act as a behavioral deterrent, not a structural one.
Standard Great Stuff foam does contain isocyanate compounds that are toxic if ingested, so a mouse chewing through regular foam isn’t having a great time either. But PestBlock’s dedicated bittering agents are specifically formulated to discourage chewing before the animal gets very far, rather than relying on the general unpleasantness of polyurethane chemistry.
For insects, PestBlock is more effective as a simple gap-sealer than as a chemical deterrent. Insects don’t chew through foam the way rodents do. Sealing their entry points with any expanding foam eliminates the pathway, and PestBlock doesn’t offer a major advantage over regular foam for that purpose alone.
Performance and Application
Both products apply the same way: shake the can, attach the straw or applicator, and dispense into gaps. PestBlock becomes tack-free in about 6 minutes and can be trimmed after one hour, though full cure depends on temperature and humidity. Regular Gaps & Cracks has a similar cure profile. Neither product lists significantly different R-values or densities in their technical documentation, and for pest exclusion purposes, insulation performance is beside the point.
PestBlock is intended for gaps up to about one inch wide, the same as regular Gaps & Cracks. It’s designed for use around pipe penetrations, cable entries, dryer vents, sill plates, and anywhere exterior walls have small openings that pests could exploit. You wouldn’t use either product for large structural voids.
When PestBlock Is Worth the Extra Cost
PestBlock typically costs 20 to 40 percent more per can than regular Gaps & Cracks. That premium makes sense when you’re sealing known pest entry points: gaps around pipes entering your foundation, spaces where utility lines pass through exterior walls, or openings along your sill plate. These are spots where mice actively enter homes, and the deterrent chemistry adds genuine value.
For interior-only projects like sealing around window frames, filling gaps behind baseboards in upper-floor rooms, or general air-sealing in an attic with no rodent history, regular Gaps & Cracks does the job at a lower price. The pest-deterrent compounds don’t help if pests were never going to encounter that foam.
Combining Foam With Physical Barriers
If you’re dealing with an active rodent problem or sealing gaps larger than a quarter inch, the most effective approach combines expanding foam with a physical barrier. For medium to large holes, pack the opening with steel wool or copper mesh first, then apply foam over it. Steel wool is difficult for rodents to chew through, and the foam layer holds the mesh in place while sealing out air and moisture. Copper mesh won’t rust the way steel wool can, making it a better choice in damp locations like crawlspaces.
Using PestBlock over steel wool creates a two-layer defense: the physical barrier stops chewing, and the chemical deterrent discourages the attempt in the first place. For smaller cracks and gaps where mesh won’t fit, PestBlock alone is a reasonable option. Regular foam alone, without mesh reinforcement, is the least reliable choice for any gap where you’ve seen evidence of rodent activity.