This is a really clear youtube tutorial about how to make a chemise, this one in particular is for a 1700s chemise but the basic design doesn’t change much between the medieval era and the victorian, so feel free to just use this one for that thousand years or so.

One of the basic foundation pieces of any historical wardrobe, the chemise goes underneath everything and soaks up your bodily juices to stop them getting on your nice (and harder to clean) clothing.

They are also necessary for going under garments that might rub or chafe if left against the skin. Don’t wear a corset or stays without anything underneath!

Link