Hoffman sizes their bottoms for the liner used so the boots that come with the thinsulate liners are too tight with the felt. You could use the thinsulate in a felt boot but would have to add insoles to fill up the void. When replacing bottoms you can switch from felt to thinsulate or thin to felt. This came directly to me from Hoffman CS.
Tested their information and is correct, Have a pr of Thins corks and a pr of Whites cowboy felts with bottoms replaced by Hoffman. Thins in the felt cowboys, liners fit well but loose on my foot. Felt in the Thins corks way tight.
Replaced the corks recently, always use anti seize , couldn’t replace some.
I use felts in my thin corks. Yes its tight initially, but they break in. I think the felt is warmer than the thinsulate. The lady at Hoffmans told me the same thing when I asked for a new felt liner and I told her, well I do it and it works for me.