There are a lot of different brands of polymer clay, these are just of the more common ones – Premo, Fimo, Kato PolyClay and Cernit. There are also several others too, including Sculpy and Pardo and some specialty clays, like for dolls.
These days they are all available on online so if you clay, can wind up with several different brands. Like always I just worked using trial and error and mixed without too much trouble since many cure at about the same temperature. Temperature seems to be a big sticking point for many clayers. Some are quite fanatical but so far I haven’t any trouble except the one time I goofed and put the temperature at about 320 F.
I said many of the clays cure at the same temperature but this isn’t quite right. According to the instructions Fimo cures at 230, Prosculpt (for dolls) and Cernit at 260 and Sculpy and Premo at 275 while Kato cures at 300. Some were designed for a higher or lower temperature but most don’t seem to. Sometimes I’ve bought a different brand just for a unique color or accent, so I didn’t plan to use it alone.
Basically you can mix any two types and use them safely, the suggestion is usually to use the lower temperature. To be honest I don’t use either Fimo or Kato much so I’ve never mixed them together, those two might make me nervous. Often I’ve mixed a firmer clay, like Kato or Cernit, to something softer. The harder clays can be a pain to condition but when mixed with a softer clay, they can let you add more details. The same idea applies to colors- Kato has a magenta that can’t be beat for mixing colors.
The real stickler always seems to be the temperature. I’ve used 2 different types of clay, unmixed, in the same piece without any issues. I’ve heard that baking a clay at a lower temperature that listed means it won’t fully cure but as long as I go above 260 and give it time, I’ve have no problem. Hell I had a solid 1 pound block cure to a brick because I left in my car in the summer.
I guess I am more right brained or is left brained the creative side – whichever it is, I tend to just do what I’ve figured out works for me. I’ve discovered some of the strict rules for polymer clay can easily be bent and even broken and still result in beautiful and strong piece.