Answering the What is this post just below.

It is just called insulation board. I would make a piece of wood or masonite that just fits into
the hole at the very top , but is longer than the hole is wide. I would drill a hole in the middle
of it, and put a stout string about 10 inches long through the hole and around a nail so it can't
pull out. You will need a flexible 1.5" wide putty knife. I would buy a small can of short fiber
body filler (Kitty Hair), Mix up about a tablespoon of it on a scrap. (About 3 drops of hardener
1/2cc)
Put some of that batch on each end of the wood backer. Stick it through the hole and, using a piece
of wire or pick, position it so it covers the back of the hole and extends to each side. pull
gently on the string to paste it on the back side of the hole. You will only have about 3 minutes
work time from mixing to "oh dang it is hard already", so get the act together before starting.
Once it is in place, put tension on it for about 5 minutes. Let it cure for another 20 minutes.
Make a new batch of Kitty hair, This time about 1/3 cup (do not measure this it is a waste of time
and everything it touches is a throwaway) this time you will need about a thimble (small, or one cc
of hardener). Use the putty knife to gently fill the depression to level, and use the rest to fill
in around the worn/weathered places shown in the picture. Clean off the putty knife while the
filler is still not quite set. Using a second putty knife is usually successful at the cleaning.
When hardened, excess can be sanded off with a disc sander on a drill, or ? don't push too hard on
it or it will break out fiber next to it. Put the siding back on, and call it good. Jim

The better you can seal air leaks, the less likely the little chewers will be to come back.

That's how they find a weak place to start chewing, they feel and smell air currents.

Keeping a well trimmed perimeter around the house also helps. Rodents don't like being exposed. Keeping weeds, stored items, lumber, firewood away from the house discourages them from looking in.

Celotex was one brand name for that fibre board, we've got as wall sheathing on our house built in the '70's. R value same as solid wood, about 1 per inch.

Down south they've got a common nickname for the stuff, but I wouldn't dare mention it here {-:

Yep, I resisted on posting that name also.
Richard in NW SC

I used to work at the insulite mill in International Falls MN where it was made. A good product in it's day, but made obsolete by Styrofoam. Originally it was made out of the pulp that wasn't good enough for paper!

To Absent Minded Farmer,

This is off-topic, but I need to figure out how your original post was created. Would you mind emailing me anything that happened in the process of posting it, and if you used Modern or Classic. That post looks like it aborted during the posting but I have no idea where to start to figure out what happened.

Thanks