lightweight/durable/blackout fabric?

I thought I'd check with your knowledgable ladies to see if you have any suggestions. I've been recruited to sew up a new curtain for my daughter's preschool for their large, half circle window. It's attached with velcro at the top during nap time to block the light so it is put up and taken down nearly every weekday each year. The current one is denim and has lasted about 5 years. It needs to be a dark color so it doesn't show dirt/stains, and needs to hold up to lots of use/washings over the years and be light weight in order to stay up with velcro and be easy to put up and take down. Oh and not too bulky as it needs to be folded up and stored when not in use. Any ideas or suggestions for something that they may be able to get more than 5 years of use out of? Thanks again.