A winding path's blocked by large surface material (7)
I believe the answer is:
asphalt
'surface material' is the definition.
(I've seen this before)
'a winding path's blocked by large' is the wordplay.
'winding' is an anagram indicator.
'blocked by' is an insertion indicator (upper walls off glass inside formal).
'large' becomes 'L' (eg in clothes sizes).
'paths' anagrammed gives 'sphat'.
'sphat' placed around 'l' is 'sphalt'.
'a'+'sphalt'='ASPHALT'
(Other definitions for asphalt that I've seen before include "Material for covering roads" , "petroleum residue" , "Bitumen" , "What you see on roads" , "that's found on the way" .)