http://www.osteopathic.org/osteopathic-health/about-your-health/health-conditions-library/general-health/Pages/plastics-microwaving.aspx http://www.osteopathic.

http://www.osteopathic.org/osteopathic-health/about-your-health/health-conditions-library/general-health/Pages/plastics-microwaving.aspx http://www.osteopathic.org/osteopathic-health/about-your-hea... says "If a plastic product is determined safe for microwave use, then you will see either a microwave-safe symbol or written instructions indicating the product is microwave-safe. The numbering system found on plastics pertains to recycling and does not indicate whether or not the plastic is safe for heating. However, Dr. Danoff warns that not all microwave-safe products are safe to use in the microwave in the same way." No elaboration on this last point other than to say don't reuse tv dinner trays. Overall I prefer to microwave glass but I'd like to know for sure one way or the other.