Quantity   Component name
2 × pieces of 100% cotton cut to 6" by 9" (15.24cm x 22.86cm)
2 × pieces of 1/4" (0.635cm) elastic (or whatever width you have/want) lifetime supply for cheap: https://www.amazon.com/gp/product/B088LNQM8G/
1 × thread
4 × pins to hold the fabric pieces together
1 × steam iron to create the pleats