Layer of polythene (3)
I believe the answer is:
hen
'layer' is the definition.
(hens lay eggs)
'of polythene' is the wordplay.
'of' indicates a hidden word.
'HEN' is hidden within 'polythene'.
(Other definitions for hen that I've seen before include "Farm bird" , "Coop resident" , "Clucking female" , "Female bird" , "Not cock" .)