Bed takes weight of material (6)
I believe the answer is:
cotton
'material' is the definition.
(cotton is a kind of material)
'bed takes weight' is the wordplay.
'bed' becomes 'cot' (cot is a kind of bed).
'takes' means one lot of letters go next to another.
'weight' becomes 'ton' (ton is a kind of weight).
'cot'+'ton'='COTTON'
'of' acts as a link.
(Other definitions for cotton that I've seen before include "Cloth made from fine hairs of seed pod" , "Fabric woven from plant fibres" , "Golfing man" , "Plantation product" , "Plant fibre for fabrics" .)