I think he said the plastic ones Chris
Yep .. I did say plastic. Plastic is best.
However ......
I've actually been reheating takeaways in (ALUMINIUM) foil dishes in the microwave for years ... without arching or sparking.

All my chinese takeaways go straight into the microwave as soon as I get home and the food zapped before I even open the lids (not the Chilli beef though).
This astounds many people, but try it. It is usually okay. :

The outside of the foil dish must be clean and dry otherwise it will spark.
I think arching/sparking is caused by impurities on or within the aluminium foil.
Nevertheless over 95% of containers I've zapped have been okay. If it does cause arching simply remove it.
SnS ;D