[alodg]

I am looking to find a definitive answer as to whether the use of solid silicone in a domestic 800W microwave is safe, in that it remains inert and doesn't retain heat for too long.

It may be that the widespread use of it in the kitchen puts an end to that question, but I'm still looking for a scientific answer to quell any doubt, which is considerable in the kitchen arena. There is precious little imperial data as the use of new silicone products to replace tried and tested metals leaves long term doubt, but the use of silicone in other industries should prove comforting.

I plan to use a silicone baking mat (which is only a few millimetres thick) inside a flatbed microwave (a particular model that needs not the turntable most models use, instead reflecting the microwaves off of the angular shaped interior in all directions) to protect the base from scuffing and scratching but need to know if silicone will heat up in direct contact with microwaves?

As the silicone is not in liquid form I don't believe it will, understanding that microwaves heat an object up by vibrating the molecules of tissue, would the sold form of silicone then simply remain at room temperature?

Another concern I have is heat retention, as objects placed on the silicone will inevitably heat up and then transfer their heat, will that spot in the microwave be under more stress if the heat remained as a result of the silicone retaining that original heat once the heat source has been removed?

I imagine that domestic microwave ovens are more robust than I give them credit for, also that thickness of the silicone is likely a key factor in heat retention and a few millimetres would likely not make much difference than the material the microwave if made from (perhaps then the silicone could relieve stress?) and that the microwave has been engineered to be reinforced in that particular area.


My final concern is the purity of the silicone, where if the silicone is not an issue then what if it were a composite, that other element then being the one of concern. I read that silicone baking mats are coated in a fibreglass exterior (not to be cut on with a steel blade!) and wonder what affect microwaves have on that material also?

It would be good to get a scientific answer to some of these questions.

[Arkcon]

Please take a moment to realize a few things.  The use and production of materials for food handling is governed by a number of agencies -- US FDA, UL and perhaps more.  They provide references to peer-reviewed research where safety under a number of conditions has been determined.  This information isn't easy to find, and its sometimes hard to follow.  But its false to claim it doesn't exist.

That said, the internet has been clogged, since its inception, with junk science rants, bad experiments, discourse that isn't even pseudoscience -- because it doesn't even make the pretense of being logically based, but instead is proud of its emotional basis.  Be forewarned, we don't allow crack-pottery here.  And when a long missive such as yours arrives, I tend to assume the person has arrived with a pre-concieved notion.  So lets work together, and get to a useful answer.

I am looking to find a definitive answer as to whether the use of solid silicone in a domestic 800W microwave is safe, in that it remains inert and doesn't retain heat for too long.

A clear statement, that asks a clear question.  Easy to follow.

It may be that the widespread use of it in the kitchen puts an end to that question, but I'm still looking for a scientific answer to quell any doubt, which is considerable in the kitchen arena. There is precious little imperial data as the use of new silicone products to replace tried and tested metals leaves long term doubt, but the use of silicone in other industries should prove comforting.

As I mentioned above, empirical data most certainly exists, and is freely available, although difficult to find and understand.  This paragraph is mostly an emotional plea, that says nothing.  Please try to be alert to this sort of thing, it can be off putting.  Perhaps you didn't expect this to be analyzed so closely, but then, why type it at all?

I plan to use a silicone baking mat (which is only a few millimetres thick) inside a flatbed microwave (a particular model that needs not the turntable most models use, instead reflecting the microwaves off of the angular shaped interior in all directions) to protect the base from scuffing and scratching but need to know if silicone will heat up in direct contact with microwaves?

If it will heat up under microwave energy, in your particular model of appliance, can be empirically tested by you.  You can map your microwave for "hot spots" (I like this method:  http://www.evilmadscientist.com/2011/microwave-oven-diagnostics-with-indian-snack-food/) or use an infrared sensing thermometer.

As the silicone is not in liquid form I don't believe it will, understanding that microwaves heat an object up by vibrating the molecules of tissue, would the sold form of silicone then simply remain at room temperature?

No, many solids heat up in the microwave.  I bought some melamine tableware (discount store) and I know that stuff will "pop" right away in the microwave.

Another concern I have is heat retention, as objects placed on the silicone will inevitably heat up and then transfer their heat, will that spot in the microwave be under more stress if the heat remained as a result of the silicone retaining that original heat once the heat source has been removed?

Hard to know.  I guess it could, infared thermometer will help you here.  Maybe after you know something, you can call the manufacturer and say, "This temperature,, for this duration, in this spot, can your appliance survive that?"  They hire teams of people just to assuage customers, they're likely glad to talk to you.

I imagine that domestic microwave ovens are more robust than I give them credit for, also that thickness of the silicone is likely a key factor in heat retention and a few millimetres would likely not make much difference than the material the microwave if made from (perhaps then the silicone could relieve stress?) and that the microwave has been engineered to be reinforced in that particular area.

A bunch of conjecture here, don't really see the point since we start with almost no information.

My final concern is the purity of the silicone, where if the silicone is not an issue then what if it were a composite, that other element then being the one of concern. I read that silicone baking mats are coated in a fibreglass exterior (not to be cut on with a steel blade!) and wonder what affect microwaves have on that material also?

Hmm ... you may have to look up what a silicone baking mat is actually made of.  I didn't know they had fiberglass in them, they seem to be just the silicone co-polymer.

It would be good to get a scientific answer to some of these questions.

Perhaps I flatter myself too much, but I believe you just have, even though I've answered nothing.  By definition, empirical data has a range of values, and only really applies to tested conditions.  Extrapolation just flies in the face of all that, yet, we still must do it from time to time.  So we only really know, that we have to ask simpler questions, just to get a limited answer.

[Enthalpy]

a flatbed microwave (a particular model that needs not the turntable most models use, instead reflecting the microwaves off of the angular shaped interior in all directions)

This is a misconception. Mirrors reflect light i some direction because of the very short wavelength. Ovens use 12cm wavelength, which a 30cm reflector diffuses, whatever its angle. And you will get cold spots in the oven cavity despite the walls angles. Moving the microwave source or changing its polarity (of done!) can linder this but not avoid it.

need to know if silicone will heat up in direct contact with microwaves?
As the silicone is not in liquid form I don't believe it will, understanding that microwaves heat an object up by vibrating the molecules of tissue

Silicone is not expected to heat strongly in the microwave field. This doesn't relate with liquid or solid. By the way, it's not a matter of water nor resonance neither. Just a matter of losses, which may relate or not with vibrations, which solids do too. In short: simple logic won't help here. The property you seek is called the tan(δ) of the permittivity ε, or sometimes it's ε"; check it at 2.45GHz or somewhere between 0.5GHz and 10GHz.

Another concern I have is heat retention, as objects placed on the silicone will inevitably heat up and then transfer their heat, will that spot in the microwave be under more stress

I don't quite grasp the worry. Oven walls are supposed to resist heat. If you mean mechanical stress, the soft material won't bring any into metal.

My final concern is the purity of the silicone, where if the silicone is not an issue then what if it were a composite, that other element then being the one of concern. I read that silicone baking mats are coated in a fibreglass exterior (not to be cut on with a steel blade!) and wonder what affect microwaves have on that material also?

Fibreglass is used for printed circuits at these frequencies thanks to its low losses. No significant effect. BUT while some silicone formulations can be allowed for food contact and even body implants, formulations can and do vary a lot, some containing for instance organotin depending on the curing process which distinguishes at least 3 families of silicones. There is no room for improvisation nor amateurism there. Ask your supplier a formulation allowed for food contact, and stick to it.

[Intanjir]

They often embed a visible glass fiber mat reinforcement in silicone mats for cooking. It is just made of little thin strands of glass.