They're always thin (7)
I believe the answer is:
veneers
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">they're always thin</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this in another clue)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for veneers that I've seen before include "Thin wooden sheets" , "Coatings of a thin layers of superior quality" , "Superficial overlays" , "Fine wood facings" .)