Model material (5)
I believe the answer is:
balsa
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">model material</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this in another clue)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for balsa that I've seen before include "Very light wood in a slab" , "Central American forest tree used to make floats, rafts, models etc" , "wood for raft" , "Lightweight timber" , "lightweight boat-builder" .)