expanding foam is basically mouse confetti... they love tunneling through that stuff.
Couldn’t agree more—expanding foam is a joke against rodents. Hardware cloth’s the way to go, but I’d argue you need to double up in some spots. Mice are relentless, especially when it gets cold. I’ve seen them squeeze through gaps you’d swear were airtight. Cardboard and duct tape? Been there, done that... but nothing beats a solid metal patch if you want to sleep at night.
Metal patching is the only thing that’s ever held up in my experience. I’ve been called out to crawlspaces where folks tried everything—foam, steel wool, even a bit of chicken wire—and the mice still found a way through. One guy had stuffed every gap with expanding foam thinking it was “rodent proof.” Six months later, there were tunnels like a hamster cage.
I’ll admit, I used to think steel wool could do the trick if you really packed it in, but those little suckers will chew right around it if they’re determined enough. Hardware cloth is solid, but yeah, double it up at corners and anywhere pipes come through. Mice have a sixth sense for weak spots, especially near old heater vents or where someone got lazy with the caulk.
Cardboard and duct tape just make their lives easier. If you want a real fix, sheet metal and screws are the way to go. Might not look pretty, but you’ll actually keep warm without sharing your house with a mouse family.