After wwll, which synthetic fabric began appearing in casual clothing?

Rayon, the new synthetic fabric developed in the 1930s. This became the number one material most often used for the creation of ladies' clothing during the War. 
I got the info from this site:
https://bellatory.com/fashion-industry/Fashion-History-Design-Trends-of-the-1040s

Ifound this on google “simply, the working conditions were terrible during the industrial revolution. as factories were being built, businesses were in need of workers. with a long line of people willing to work, employers could set wages as low as they wanted because people were willing to do work as long as they got paid.” i hope this you for what your looking for.

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