Note variable length with both old and new fabric (5)
I believe the answer is:
nylon
'fabric' is the definition.
(I know that nylon is a type of fabric)
'note variable length with both old and new' is the wordplay.
I cannot really see how this works, but
'note' could be 'n' (abbreviation) and 'n' is present in the answer.
'variable' could be 'y' (algebra) and 'y' is found in the answer.
'length' could be 'l' (abbreviation in geometry) and 'l' is found in the answer.
'old' could be 'o' (abbreviation) and 'o' is located in the answer.
'and' could be 'n' (common abbreviation for 'and') and 'n' is present in the answer.
No letters remain.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for nylon that I've seen before include "Artificial yarn/fabric" , "Hose" , "Man-made fibre" , "Tough synthetic material" , "Synthetic material used in textiles" .)