Sit-upons are a Girl Scout tradition. I think girls have been making them since the 1950’s, maybe longer. I remember making a sit-upon as a Brownie, and I loved sharing the tradition with my Daisy/Brownie Troop recently.
When I researched the materials used for sit-upons, many sites recommended using flannel-backed tablecloths. I remember using something similar to make mine as a Brownie. My coleaders, who organized our sit-upon making, picked up flannel-backed plastic fabric which ended up being too thin. A few sit-upons ripped at our meeting. Using the duct tape to bind the sides together did work well.
I decided to make my own at home since I loved the idea, just not the execution. While at Jo-Ann Fabrics, I found clear, heavy-duty plastic in the clearance bin, thick enough to be immune to ripping. I found the carpet padding at Ikea, and picked up 2 packages. I like the carpet padding because it won’t fall apart when wet.
Place the carpet padding in the heavy plastic and fold up the sides. Tape in place.
Fold up the bottom like an envelope and tape in place.