I've just returned home from Washington to find an 8cm split in one of our rigid suitcases, presumably where a sharp-edged case was pushed against it in the plane or during handling.   The case is made of some sort of vacuum-formed Polypropylene, about 1mm thick.   It's not worth claiming on insurance: it's five years old, scuffed, and the hassle and no-claims issues make it a non-starter.  However, it's worth spending twenty quid to keep it going.