Not a bike camping situation, and the attached site has grphic photos.

http://urbanlegends.about.com/librar...ear_attack.htm

These guys were armed, and all it would have taken to survive this attack unharmed would have been a little more time to deploy the arms. Even poly hard plastic is hard to bite through at the outset. I am not sure that folks who are scared of this kind of thing (you should be scared of polar bears, but you should not encounter them many places one is likely to take a bike), are going to be placated by bags. And the Bear bags are not approved in some parks because the bears can gain access to them. The bags just stop the bears from eating the contents, not chewing the heck out of them. If they worked, they would solve the problem of the bears getting at food, they do not keep the bears from destroying your food. They are going to be breaking your bones if they get you wrapped up in a tent made of that stuff.

There is also the idea of scent control. A hard object can control scent which is essential, and also hide movement and noise better.

I am not personally serious about the bear thing, I am just pointing out things a hard shell does that a soft one does not. Maybe it just keeps raccoons out of your stuff...