… of the 1770’s was linen; specifically flax-based linen. Linen acts much like cotton, but it is stiffer and has a shiny side to it, a rough feel, and has a more open weave. Both cotton and linen let air flow in and out, so they are very comfortable to wear and work in, and easy to clean.
(Images: linen then in a sketch of a working class woman, and now historic re-enactor of lower class in linen)