Thoughts on the R-value of a wasp nest vs fiberglass?

I found a few of those 'paper footballs' in the soffits of my workshop last winter. I actually did a rough check with my Flir thermal camera and the spot with the nest showed about the same heat loss as the sections with old, slumped rockwool. It’s basically wood pulp and saliva, which isn't too far off from the cellulose insulation like GreenFiber that I used in the attic.

It’s probaly around R-3 per inch if it's dry and intact, similar to dense-pack cellulose. But the real problem isn't the thermal performance; it's the structure. When I left a nest in my mudroom wall, the humidity from the shower started making the paper go soft and moldy after about two years. Plus, even if the wasps are gone, dermestid beetles or larder beetles love to move into the old larvae casings and leftovers inside.

I ended up pulling mine out and replacing it with Roxul Comfortbatt. The R-value might be there, but the risk of attracting a secondary infestation or dealing with rot just isn't worth the few bucks you save on fiberglass.

I disagree that it's anything like blown-in cellulose. Brands like GreenFiber are treated with borates and shredded to a specific density to stop airflow. A wasp nest is mostly empty space with thin, brittle walls. Those large air pockets actualy allow for convective loops inside the wall cavity, wich kills your thermal performance. You might get an R-2 out of it if you're lucky, but it's nothing compared to a tight pack of mineral wool.

I had a similar situation in my workshop and found that once those nests get damp, they turn into a soggy mess that attracts carpet beetles and silverfish. I ended up ripping out the sections and replacing the nests with Rockwool Comfortbatt. The difference in the draft was night and day. Even if the R-value seems okay on a thermal camera for a moment, the lack of a proper air seal and the risk of rot makes it a major liability.

Also, don't forget the smell. Old nests can hold onto moisture or pheromones from the colony. I’d pull it out, vacuum the cavity with a HEPA vac, and spray a bit of Concrobium to make sure you aren't leaving a buffet for the next generation of pests. It’s better to have a clean, predictable material in your walls than a biology project.

I'm pretty clueless about the physics here, but if those air pockets are causing 'loops' that ruin the insulation, coud you just smash the nest flat to make it denser? I'm wondering if the material itself is acutally decent if it's packed tight like the cellulose you guys mentioned. Also, does the age of the paper matter? I’d imagine it gets relly brittle and breaks down after a few years, but maybe it stays the same if it’s kept dry in the wall?

Smashing it is a waste of time. Wasp paper is super flammable once it dries out, and it’s basically a welcome mat for termites. If you want that high-density paper performance without the fire hazard, you shoud just pull it and use Applegate Stabilized Cellulose. It’s treated with borates so pests won't touch it, and it actualy stays put without settling. It gives you a way better seal than a bunch of old bug spit ever could.

I'm not so sure it's as simple as just checking the R-value of the pulp. Have you ruled out how much air is leaking thru the gaps around the edges of that nest? It's not like spray foam that expands to fill the corners; it’s a loose fit at best. You're probably losing more heat through the air bypass around the nest than you're saving through the material. Also, have you considered how it handles vibration? One good door slam or some seasonal shifting and that brittle paper is just going to crack and leave you with big thermal voids anyway.

While the previous points regarding convective currents are sound, one must consider that the thermal conductivity of the specific wood-pulp-to-saliva ratio varies significantly based on the foraging species, as a European hornet nest utilizes much coarser, more lignified fibers than your standard yellowjacket nest. Furthermore, the hexagonal geometry of the inner brood comb functions as a series of stagnant air cells that could achieve a respectable R-value if the exterior envelope remained hermetically sealed against the studs to prevent bypass. However, the total absence of borates means the material acts as a hygroscopic sponge, eventually reaching a moisture equilibrium that facilitates the rapid degradation of the cellular integrity of the paper itself.