Bumroll skirt support suitable for the 16th-18th Century.
 
Bum rolls, or simply "rolls", were used to create the illusion of wider hips when worn under several layers of skirts. They also helped keep the hem out from the feet to ensure one would not trip whilst walking.
 
Your roll will be made of linen or cotton, though calico is used in the image.
Later pictures show how the outer skirts look worn over a bumroll.