Former college, filthy place, to mostly renovate insulation, perhaps (11)
I believe the answer is:
polystyrene
'insulation perhaps' is the definition.
I can't tell whether this defines the answer.
'former college filthy place to mostly renovate' is the wordplay.
'former college' becomes 'poly' (polytechnic).
'filthy place' becomes 'sty' (I've seen this before).
'to mostly' means to remove the last letter (most but not all of the word).
'renovate' becomes 'renew' (I've seen this in another clue).
'renew' with its last letter taken off is 'rene'.
'poly'+'sty'+'rene'='POLYSTYRENE'
Can you help me to learn more?
(Other definitions for polystyrene that I've seen before include "Synthetic resin making lightweight packaging" , "Lightweight synthetic material" , "Hard plastic" , "Light synthetic resin" , "Synthetic resin for packing, insulation" .)