Synthetic Fiber
noun
Fibers you join together to make more, stronger fibers, they turn into synthetic fibers.
Note that this is an abbreviation of the specialist term 合成繊維, and it mostly comes up in industrial contexts.
This is a jukugo word that uses the on'yomi readings of the kanji. You should be able to read this on your own.
原油安やナフサ安を受けて、合繊の価格も下落しています。
We receive cheap crude oil and cheap naphtha and the price of synthetic fibers is also falling.