Some surprisingly crass material (5)
I believe the answer is:
lycra
'material' is the definition.
(I've seen this before)
'some surprisingly crass' is the wordplay.
'some' indicates the answer is hidden within the clue (some parts of the word are used).
'LYCRA' can be found hidden inside 'surprisingly crass'.
(Other definitions for lycra that I've seen before include "Sports clothing fabric" , "Elasticated synthetic material" , "Elastomeric material" , "Stretch fabric" , "Sports clothing material" .)