Will Insulation Stop a Bullet?

When talking about overpenetration in home-defense scenarios, the main concern is that bullets may pass through walls and cause injury to someone on the other side. And apparently there are folks who attribute fiberglass insulation with bullet-stopping capabilities. So Paul Harrell has decided to demonstrate for all to see whether the most-common wall insulation in the USA (fiberglass “wool”) has any value for stopping bullets.

There are people who strenuously assert that this stuff is some kind of bullet stop. Well… let’s put that to the test.

To give the fiberglass its best chance, he starts with a wimpy round: 25 ACP — firing hollowpoints, which should penetrate less than “hardball” (a.k.a. FMJ) bullets. Predictably, it fails.

He then fires a typical small 9mm personal-defense pistol through a chronograph with and without insulation “slowing” the bullet. With average velocities of 1100 vs. 1081 fps, we can see that the bullet is — maybe — slowed by a mere 19 feet per second… which ain’t much.

Insulation as a bullet stop? Yeah, no.

Russ Chastain

Editor & Contributing Writer Russ Chastain is a lifelong hunter and shooter who has spent his life learning about hunting, shooting, guns, ammunition, gunsmithing, reloading, and bullet casting. He started toting his own gun in the woods at age nine and he's pursued deer with rifles since 1982, so his hunting knowledge has been growing for more than three and a half decades. His desire and ability to share this knowledge with others has also grown, and Russ has been professionally writing and editing original hunting & shooting content since 1998. Russ Chastain has a passion for sharing accurate, honest, interesting hunting & shooting knowledge and stories with people of all skill levels.