Part of the Antique Fabrics series.
A heavy woolen cloth, dyed brown with extracts from the butternut tree.
If you want to play a Confederate soldier in the US Civil War, you’re going to learn a lot about butternut, as it was a widely-used homespun fabric used to replace official-issued uniform jackets and trousers as they wore out.
It’s also the subject of some very fierce debates regarding the actual color of butternut fabric. The surviving samples have oxidized over the preceding 160+ years, which means what you see at a museum does not resemble what was worn at the time. Some re-enactors have taken to dyeing their own fabric with a home-made nut dye.
Should you get involved with a project that requires that level of accuracy, find yourself some experts (more than one, ideally!) for guidance regarding what to use. You’ll probably get a different opinion from each person you consult, but at least you’ll have a range of options.
My reading on Civil War re-enactment / living history forums tells me that there is some polyester fabric out there that’s offered up by some sellers as a viable substitute for wool butternut, but it is not well thought-of. Nor would I recommend wearing a uniform made from a heavyweight polyester if you have any alternative.