Had to look up tar paper never realised It was roofing felt people actually make windows out it in this day and age?
I think bituminous paper has been conflated with actual felt, which is a sheet of animal fur and probably the product of choice before petroleum science. There was a builder online years ago who was a proponent of actual felt as a building wrap since it was vapor permeable but became impermeable to water with exposure (as the animal hair expanded with wetting, making the matrix impassable. Hair swelling is also why you don't use a bristle hair brush with water based paints). Can't remember what his objection to Tyvek was but the dude was proudly dinosaurish about it and insisted he was right.
Seems likely that merchants just kept calling any roofing underlay "felt" since that's what everyone knew it as. Probably got to the point where if a guy asked for felt underlay, and they gave him actual animal felt, he'd say wtf is this, I want some roofing felt, lol. Kind of like how most yanks will ask you for tin foil, and you hand them al foil, they'll say thanks that's exactly what I wanted.
Idk what Melvin is talking about. You can't make a window out of tar paper. A window is something which lets light in and you can see through when it's closed. That's how glass works, Vince.
