Synthetic Fibres
Noun
かせん
掃除には、化繊箒を使っています。
I use a synthetic fiber broom for sweeping.
Fibers that have been changed from other materials are synthetic fibers. They aren't natural because they were something else once. Like plastic, or kittens.
This is a jukugo word that uses the on'yomi readings of the kanji. You should be able to read this on your own.