The most common and most likely answer to this crossword clue is the 5 letter word BALSA
I've seen this crossword clue in The Guardian
B
A
L
S
A
More clues leading to the result BALSA
- Light timber that’s a piece of cake to turn over?
- Wood resin running short
- A second dog climbing tree
- Some cannibals appearing in wood
- Light timber a hunk hauled up
- Light wood, a thick piece turned over
- A piece of cake being raised in a wood
- Tree ointment when scratching bottom
- Send back a large piece of lightweight material
- A hunk climbing in wood
Buddy explains!

The straight part
We know that "lightweight material" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case lightweight material = balsa.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 BALSA mean?
BALSA noun- A large tree, Ochroma pyramidale, native to tropical America, with wood that is very light in weight.
- The wood of this tree.
- A raft or float, used principally on the Pacific coast of South America.