These are recycled / used photosensitive bags. They were used as a packaging for photosensitive paper. Do expect some/many flaws and signs of use.
Note : The effectiveness of any particular bag depends on the intensity and electric potential of the X-ray generator, and the film speed. The inspection process may be triggered by a lead bag on the scanner screen. In a typical airport surveillance situation, the baggage may be pulled aside for additional inspection.
It is said to weaken the X-rays though, as mentioned, it depends on the X-ray generator and the film speed. We always recommend to hand carry films instead. We also have x-ray bags made to protect your films. Check them out.