The 50-pack of NFF35-120 Negative File Folders from Print File is made from 10-pt. buffered cream-colored folder stock that is acid- and lignin-free. Each archival one-size-fits-all envelope accommodates 35mm film strips with six frames or 120 strips with four frames. The Negative File Folders are compatible with the Negative Strip Flip-Top Box, in which the envelopes fit exactly. Twenty-five left and right tabs each are included to help identify the contents or subject matter of the envelope. These envelopes have passed the Photographic Activity Test (PAT), meaning they are suitable for long-term storage and won't yellow over time.