Depends. There are heavier lead bags now than there were several years ago, and they do offer some protection. I often use them for 4x5" and smaller formats in my carry-on luggage. I would not put film in checked baggage, even in a lead bag. Sometimes the inspectors will ask to see the contents of the bag or run the film without the bag, but often, if they see the bag with a lot of other photo equipment and nothing else looks out of the ordinary, they'll let the film through without asking to see the bag, or they might just do an explosive swab. I figure that if I might be traveling and it cuts down on the cumulative exposure, then that's a good thing.