Clue: Polymer stored by foxy landlady (5)
Answer: XYLAN
Explanation: Definition: Polymer

Hidden in [*stored by*] "fo**XY LAN**dlady"
 
*Not in Chambers, but according to Wikipedia, **xylan is a type of hemicellulose, a polysaccharide consisting mainly of xylose residues, found in plants, in the secondary cell walls of dicots and all cell walls of grasses.