For safety reasons, hot air balloons are only allowed 400-500 hours of total flight time. After that the balloon, which may begin to leak, is decommissioned; the basket must be attached to a freshly-made balloon.
That leaves a helluva lot of fabric for the balloon operator to get rid of. A typical 77,000-cubic-foot hot air balloon uses around 1,750 square yards of rip-stop nylon that cannot legally be used to make another balloon; it's no longer of any use to the operator. "But while they're long past their days in the sky," writes UK-based Virgin Balloon Flights, "there's plenty of life left in them for epic upcycling projects."
The company is seeking applicants to send them a proposal for what you'd make out of decommissioned balloon fabric. If they like the project, they'll donate the fabric to you (from 3 square meters up to an entire freaking balloon, which can weigh hundreds of pounds).
Virgin will only ship to UK-based applicants. If you live elsewhere and have an idea for the stuff, it might be worth contacting a local balloon flight company to see if they'll give you their decommissioned balloons. Also, ID students, if you're looking for a project that will repurpose a massive amount of material, here you go.