Outdoor fabrics need to be a number of things to be able to do their job properly. Polyester fabric is Water-Resistant, durable and UV-resistant, and it can be washed.
Blended fabric contains multi-filament and elastic yarns coated, resistant to water, UV and heat degradation, suitable for outdoor exposure. It has elastomer yarn, set in the filling direction, and can be combined with acrylic, polyester, polyamide, deformed filament and other yarns. Or other uncoated filament.
A simple wipe-down with soapy water now and then will keep it looking great.