What were these bags used for?

As part of the extensive arrangements to prevent potential contamination of lunar samples prior to examination by scientists, and to protect the Earth from potential "Moon germs", provisions were made to clean and bag all equipment exposed to the lunar surface. The Apollo Lunar Surface Return Containers (ALSRC) filled with lunar soil and rocks were among the most important items to be returned from the Moon. As a result, specially designed Beta-cloth bags were provided and stored in the Command Module to isolate the "rock boxes" prior to transfer from the Lunar Module. Prior to being placed inside the decontamination bags, the rock boxes were vacuumed and brushed.

Although decontamination requirements were relaxed following the Apollo 14 mission, great care remained necessary to control the amount of lunar dust in the Command Module on the return flight to Earth and to keep the lunar samples as pristine as possible. This bag was flown on the Apollo 15 mission.