How many letters does the top answer for “a covering material made of glass fibers in resins” have?

The most common answer is fiberglass (10 letters).

Crossword clue: a covering material made of glass fibers in resins

2 answers found in Letterora's clue database (Wikidata facts, Open Trivia DB, WordNet and Webster definitions — all licensed sources).

fiberglass 10 letters wn-def

a covering material made of glass fibers in resins

fibreglass 10 letters wn-def

a covering material made of glass fibers in resins