Michael Atkinson has had trouble because of damage when he carries his horn in a soft gig bag, owing to his alarming tendency to bump the bag against chairs, on subways and busses. Not to mention the damage that arises when he drops it. He suggests switching to a hard gig bag.
This may help, but it will not solve the problem. The problem occurs mostly because the horn is so hard. This is a situation similar to many which arise in the physics of bumping, or bumpogenics. Basically, during the bumping interaction, the object (the bumper) and the horn (the bumpee) exert compressive stresses on the delicate material of the gig bag. The resulting strains cause the horn and the object to emit elementary particles called bumpkins which are responsible for the actual damage.
Luckily, there is an easy cure. Switch to a soft horn! Since I did this about six month ago, the damage to my gig bag has been greatly reduced.
Gotta go,
Prof. Cabbage