Against stocking too much material (6)
I believe the answer is:
cotton
'material' is the definition.
(cotton is a kind of material)
'against stocking too much' is the wordplay.
'against' becomes 'con' (I've seen this before).
'stocking' indicates putting letters inside ('stock' can mean 'carry' or 'contain').
'too much' becomes 'ott' (short for 'over the top' - informal British).
'con' placed around 'ott' is 'COTTON'.
(Other definitions for cotton that I've seen before include "Fabric woven from plant fibres" , "Fabric made from tropical plant - old man river don't plant it" , "Old golfer" , "Cloth made from fine hairs of seed pod" , "Plant, its fibres for yarn" .)