As someone who was there at the beginning of the man made fabrics and fusible interfacing's for the tailoring trade. I can tell you it was very hit and miss. The multiple tailors may have been developing techniques for the interfacing’s, with the floating chest pieces and fused break lines, but the smaller boys were trying to fuse canvas's with the tailors iron, without any knowledge of timing or pressure to give to the fusible canvas. The results of all this haphazardness could be seen when someone sent a suit to the cleaners, the fusible interfacing’s just separated and left terrible ridges down the front of the garments. Collars were being cut for the first time with a separate stand and fall, and both pieces were being fused with stiff canvas (the result can be seen on the suit in the picture with the stiff lapels.) The earlier fusible canvas was a gummed resin which, after a certain length of time (if the canvas was left unused) would turn into a powder in places,(when you unrolled the canvas, it was like shaking off, dandruff!)
As for the man made fabrics. One advert in the late 50's early 60's, showed a man in a smart suit, diving into a swimming pool and swimming the length of the pool. Upon emerging from the pool, the water was shed from the suit, and it looked as pristine as it was before he entered the water.
The earlier 'Terylene' suits were very stiff and hard to handle. There was one product 'Acrylan' which was as stiff as cardboard when the suit was finished. If you held a piece of the fabric in your hand and held a lighted match to it, it burned and dripped like tar! Of course, this was in the early days. As these problems were discovered, things changed and techniques were developed to improve things, but never to the standard of the wool and worsted fabrics from the satanic mills!