Polyester is a good choice for cushions. Polyester holds up well, is washable, doesn't shrink like cotton. I have been using polyester battings in kids quilts for years. I use many different batts, there is such a great variety now, you can find the perfect choice for every project. I use blends, 80% cotton/20% poly is a popular blend, I love wool batts, there's silk, bamboo, dream green- which is made from recycled plastic bottles, orient blends, lots to choose from. Try different ones as you get the chance and find what you like as you continue on your quilting journey