The most common and most likely answer to this crossword clue is the 7 letter word PLYWOOD
I've seen this crossword clue in The Daily Telegraph
P
L
Y
W
O
O
D
More clues leading to the result PLYWOOD
Buddy explains!

The straight part
We know that "boarding material" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case boarding material = plywood.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does PLYWOOD mean?
PLYWOOD noun- Construction material supplied in sheets, and made of three or more layers of wood veneer glued together, laid up with alternating layers having their grain perpendicular to each other.
- A specific grade or type of this construction material.
- To fit or block up with plywood.