Fancy slipper material, that's clear! (5)
I believe the answer is:
glass
'fancy slipper material' is the definition.
'glass' can be an answer for 'material' (I have seen 'Vitreous material ' mean 'glass' so perhaps 'material' could also mean 'glass'). I'm not certain of the 'fancy slipper' bit.
I cannot understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for glass that I've seen before include "Transparent stuff" , "Container for drinking from" , "Perhaps schooner" , "Transparent solid" , "Greenhouse material" .)