There are many different vinyl and fabric materiel's that can be used for interior and exterior cushions. It all depends upon your pocketbook and how you want your boat to look. For exterior cushions, you need a material that will holdup to the sun, salt, water, and bird droppings. If you have the dropsy's or expect a lot of little ones, then you might want a material that will hold up to food and beverage spills. My grand kids have been pretty rough on my cloth cushions. There are different grades of vinyl material, as well as different grades of fabric material. Sunbrella seems to lead the pack for fabric material, and they also make vinyl/acrylic materials. Sunbrella will be more expensive than the material/vinyl you can get at Joann Fabrics. Many small boat owners carry over the fabric used on the outside to the inside of the boat, although it can be different. For interior cushions, you should consider how they will be used (e.g. wet bathing suits, dropsy's, little ones, decor, etc.). You do not have to have marine fabric for interior cushions. Regular upholstery material can work fine. There are lots of possibilities. Have fun.