Pale yew, so good now and again as boarding material (7)
I believe the answer is:
plywood
'boarding material' is the definition.
(material used as boarding)
'pale yew so good now and again' is the wordplay.
'now and again' indicates alternate letters (letters taken on a regular basis).
'pale'+'yew'+'so'+'good'='paleyewsogood'
The alternating letters of 'paleyewsogood' are 'PLYWOOD'.
'as' acts as a link.
(Other definitions for plywood that I've seen before include "Strong laminated board" , "Board made of several thin layers" .)