Hi James the chin cup I have is flexible...due to long period of storage and lack of use most likely!! but it seems to be made of the of the type of plastic that with a little age and UV damage would become very brittle!!! the dealer I bought mine from had several shell liner combos and a huge stack of just liners!!! some had chin cups missing others already exhibiting crack damage but some were mint!! ..., but at £3 each either way ..you couldn't really complain!!! just wish I had bought some now!!!..... alias funds had run out at that point!!! and the last time I looked on his stall most had already gone!!!