It's more foundation piecing or strip piecing than paper piecing. You can use any kind of fabric cut in strips. Muslin is always a good choice, or if you have some "why did I buy that" fabric, use it for your foundation, or you can use a nonfusible foundation (like a lightweight Pellon). Some people use fabric softener sheets that have already been used. Press them flat with a warm iron. Jenny Doan has several tutorials about strip piecing.