Material from Web in plan approved to hold crowd back (8)
I believe the answer is:
gossamer
'material' is the definition.
(gossamer is a kind of material)
I can't explain the remainder of the clue.
Can you help me to learn more?
(Other definitions for gossamer that I've seen before include "Very finest textured silk" , "Delicate filmy material" , "Material spun by spiders" , "Filmy threads seen on hedges" , "Filmy floating cobweb" .)