[chris (OP)]

What is the plastic material used for microwave-able and oven bake-able ready-meals?

[RD]

poly(ethylene terephthalate), PET ...

If crystallizable PET is used, the trays can be used for frozen dinners, since they withstand both freezing and oven baking temperatures.

https://en.wikipedia.org/wiki/Poly(ethylene_terephthalate)#Uses

[damocles]

I have just gone to the pantry and looked at one of my packages -- the polymer used in that package is polypropylene.