"the burlap sack of straw that was a mattress"
Burlap (Hessian)
Public DomainBurlap (Hessian) - Credit: Public Domain Pictures on Pixabay

Burlap (hessian) is a material woven from jute or sisal fibres. It tends to be rough and coarse, and so is used for sacking and other practical uses rather than clothing or decoration.

The rough burlap and straw mattress is just one of the unpleasant elements of the ranch hands’ life in the bunk house.