we repurpose fabric as well, from what i could see on the gov website it is legal to state the the fabrics have been repurposed and the fabric content unknown.. or these are the suggested phrasing by the gov ....
Made of clippings of unknown fiber content
*100% unknown fibers — rags
*All undetermined fibers — textile by-products
*100% miscellaneous pieces of undetermined fiber content
*Secondhand materials — fiber content unknown
- you can check this out at
http://www.ftc.gov/bcp/edu/pubs/business/textile/bus21.shtm#fiber