Thanks for your question. In this case, preservation quality refers to a material that has been tested or certified so that we are sure it does not off-gas (emit) any volatile pollutants. These pollutants are volatile (sometimes odorous) molecules from manufacture or from the ageing of the material that can cause damage to different materials in your collection. Conservation labs refer to the “Oddy test,” which is an empirical test performed to check the effect of small swatches of material on metal coupons in a closed environment, and more info can be found here on the conservation wiki:http://www.conservation-wiki.com/wiki/Oddy_Tests:_Materials_Databases.
Oddy tests results are interpreted after a period of accelerated ageing, and conservators then rank materials as unacceptable, acceptable for short term uses, or acceptable for long term uses (like your storage question). Some materials which have been tested are listed on the wiki, however, this test is limited in that it tests specifically the effect on metals (usually copper, silver, and lead) while other collections materials may be sensitive to other pollutants. Manufacturers can also change production methods without changing product names or indicating changes in any other way. Low VOC (volatile organic compounds) and “odorless”are two manufacturers terms that are related, but we often like to test the materials ourselves to be sure. If you are unable to find a carpeting type material that has been tested and seems to meet your needs you might substitute another inert material such as polyethylene foam sheeting (Volara), which would likewise cushion the bottom of your storage area. Sheet Volara or other polyethylene sheet materials are often available from archival and conservation suppliers on large rolls, so might fit your intended purpose well as you could quite easily cut it down to fit the size of your bins.
Good luck and please let me know if this has answered your question or if you’d like more information.