Premo: Hardens in oven at 275ºF (130ºC) for 30 minutes per ¼" thickness.
Cernit: Bake in preheated oven at 215-270º from 5-20 minutes depending on model size. Important - if you find Cernit either too soft(1) or too hard(2) for modeling, (1)warm in a preheated oven at 120ºF for 15 minutes and then allow to aircool; (2)warm in preheated oven at 120ºF for 5 minutes, and start to work immediately.
Fimo Classic: Easy to harden in the oven (20-30 minutes, maximum 265ºF. Use a domestic oven thermometer to observe temperature. Do not inhale baking fumes.
Fimo Soft: Harden in home oven at 265ºF/130ºC for approximately 30 minutes.
Sculpey III: Better than clay - hardens in oven. Bake 10-20 minutes at 275ºF in home oven.
Sculpey Modeling Compound: Sculpey bakes permanently hard in your home oven, 15-20 minutes at 275ºF.
Super Sculpey: Bake on ovenproof glass in 275ºF (130ºC) oven for 15 minutes per ¼" (6mm) of thickness. DO NOT USE A MICROWAVE OVEN. Avoid overbaking. Use good ventilation while baking.
The above are Manufacturers' Recommended Baking Instructions