Given the task definition and input, reply with output. In this task, we ask you to rewrite a sentence in simple English without changing its general meaning. Essentially, you want to make the sentence easier to read by using simpler words, utilizing more straightforward sentence structures, and omitting non-essential information etc.

Glass fibers are therefore used as a reinforcing agent for many polymer products ; to form a very strong and relatively lightweight fiber-reinforced polymer ( FRP ) composite material called glass-reinforced plastic ( GRP ) , also popularly known as " fiberglass " .
It is used as a reinforcing material for many polymer products .