I'm deciding what kind of insulation to use in a new detached home office. Packrats are a major problem in my area. It's a constant battle to keep them out of the floor insulation in my house.

Is denim insulation more inviting than fiberglass to packrats and other pests? Or to put it another way, is fiberglass a deterrent?

  • YMMV: "There is no test method to determine whether or not any product is rodent resistant. ROXUL’s reputation as a rodent-resistant insulation is mainly based on word of mouth and lack of negative feedback from numerous customers who use our products in 'cottage country'." - I've seen rat runs going up fiberglass batts, so that's a 'no'.
    – Mazura
    Commented Mar 14, 2017 at 2:03

3 Answers 3


To add to the other answers; Mice seem to like fiberglass. I have found nests in my grill, and under a rain barrel that were made from fiberglass they've managed to collect out of my house. Mice have managed to get into my basement and nest in the fiberglass batts on the basement ceiling many times over the years.

I try to air seal the foundation sill area when I can. I feel that if they can sense the warm air leaking they will try harder to find a way in. PestBlock (mentioned by KCasper) is a new product. I've bought a can.

I've been told that regular expanding foam is not something that rodents have trouble chewing through. Another technique is to stuff steel wool in the crack and foam that in. Rodents don't like chewing on steel wool.


You're going to mostly get anecdotes with this question, so here's mine. Chipmunks and mice, the most common home invaders in my area, don't seem to be slowed down by fiberglass. If there's a way in, they'll get in, and they'll make a tunnel to where they want to be, and that's the end of the story.

That being the case, I'd think that some nice soft recycled Girbauds would tend to be more inviting. It's all moot, though. A hole is a hole. Plan on something besides your insulation waging the battle against pests.


Only PestBlock spray foam is truly rodent resistant out of types of insulation. That stuff is too bitter for anything to go through it. It is also way to expensive to use for more than blocking holes. http://greatstuff.dow.com/product/pestblock.htm

The only way to truly stop rodents is to use anti-rodent building techniques. http://icwdm.org/handbook/rodents/rodentexclusion.asp

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