Except metal materials, plastic like Acrylic and PC are the main material for manufacturing smartphone cases, and when talking about plastic cases, though sounds strange to many, PMMA would be the very first material to be mentioned, as it's hard and durable when being made into products.
Advantages of Acrylic material smartphone cases are know as hard, durable, good transparency and harmless, while these cases would cost high and the market is full of copycats, which is not ideal to users.
To tell the truth, those cheap Acrylic cases are not worth buying because they are usually combinations of real Acrylic with ABS material inside of bad quality, if heated while charging processes, these cases would easily go wasted. Another reason of my suggesting not to buy these cases is that market is full of copycats, so that people would easily run into traps set by sellers, buying fake Acrylic smartphone cases at high prices.
Though not popular in market due to its price, Acrylic is a good material for manufacturing phone cases, and when price gets down gradually, Acrylic smartphone cases would be much more popular than they are nowadays.
Another material to talk about is PC, which is known as cheap and strong versatility, meanwhile, PC could easily be processed with different technics and artworks, but still PC material has its own weakness like it's not wearable and durable, yet feels not good and firm.
PC material goes well in different fields and goes even better in the field of phone cases, there are many manufacturers supplying PC smartphone cases due to the cheap cost and low technical requirements. PC materials could be both soft and hard, but due to its weakness, people would rapidly change their PC cases, and maybe that's one of the reason PC case goes best in market.
For both these two material smartphone cases, you can refer to http://www.mocel-case.com/products for certain products and detailed information.