There isn’t a single blanket fabric that makes it suitable for picnics. Whether it’s a warm blanket made from fleece or a lightweight blanket that contains polyester only, you will most likely be able to use it as a picnic blanket. That said, you’ll be better off with a blanket that has a waterproof or water-resistant lining. This way, you’ll be able to use it on a variety of surfaces without worrying about damaging the blanket.