A reader posted a comment: ”At 392 degrees F silicone mats release trace amounts of formaldehyde. Higher the heat, higher the amounts of formaldehyde.”
Though I continually am searching for scientific data on the health effects of silicone, this was news to me.
But having the clue that silicone releases formaldehyde, I was able to find information on this.
In fact, Dow Corning issued a fact sheet Formaldehyde Generation from Silicone Materials
The Executive Summary says
Exposure of silicone products to high temperatures in air can give rise to formaldehyde. However, compared to some organic materials such as mineral oil, silicones release only a fraction (about 1%) of the formaldehyde, presenting a significant reduction in the potential exposure to this hazardous chemical.
They go on to refer to a study that shows the temperature at which formaldehyde is released from materials depends on the type of material being heated. It costs $50 to read this study, so I didn’t read it.
Dow Corning states that where there is prolonged heating of silicones or any other organic materials, “it is important to ensure that adequate ventilation is provided.”
This wasn’t very informative, but I continued to search and found Formaldehyde Generation from Silicone Rubber. I’m going to now give you a paragraph from this paper that explains how formaldehyde can be released from silicone. It is fairly technical, so I’ve edited it a bit and divided it into pieces to make it easier to read.
Silicone rubber is a polymer consisting of an inorganic siloxane (-Si-O-) backbone and two organic functional groups bonded to each silicon atom.
The organic groups are most often methyl, but may include vinyl, phenyl, hydrogen, hydroxyl and/or trifluoropropyl.
The type and quantity of organic functional group is varied to impart certain physical and/or chemical properties to the polymer.
Most industrial grade silicones contain methyl groups with a few mole percent of vinyl groups. The methyl (-CH3) groups are largely responsible for formaldehyde generation during thermal oxidation.Thermal oxidation of methyl groups begins at 149o C [300o F] with the formation of a peroxide on the methyl group followed by scission of the Si-C bond leaving a free radical on the silicon atom and a departing peroxide. The peroxide decomposes to a hydroxide ion and formaldehyde.
A portion of the formaldehyde can decompose to carbon monoxide, hydrogen, carbon dioxide, and water. It is this portion of the mechanism that gives rise to the volatile organic products of the decomposition.
The hydroxide ion and the free radical silicon atom can react with each other, or with other methyl groups, eventually leading to the decomposition of the methyl groups and the formation of non-volatile silicon dioxide.
In addition to the volatile organic products listed, trace amounts of methanol and formic acid can also form during thermal oxidation.
Here are the VOCs generated during thermal oxidation of a typical silicone rubber containing only methyl function groups.
The rate at which thermal oxidation of silicone rubber generates formaldehyde depends on the oxygen content of the atmosphere and temperature. Formaldehyde generation occurs only where oxygen is present. Higher temperatures increase formaldehyde generation.
The paper goes on to state that silicone ribber is not the only material that generates formaldehyde during thermal oxidation. Dow Corning measured formaldehyde generation rates of various materials, summarized in the table below. 200 degrees C is about 400 degrees F. This would only be an issue in a situation like putting the material in an oven to bake it, or using it in an industrial application. These materials would not encounter 400 degree F heat in a home unless there was a fire (and then the health effects of smoke inhalation would be greater than any exposure to formaldehyde).
By contrast, Dow Corning measured a “high consistency silicone rubber” to generate formaldehyde at these rates:
< 5 µg CH2O/g-hr at < 197o C [386o F]
245 µg CH2O/g-hr at 225o C [437o F]
1418 – 4627 µg CH2O/g-hr near 250o C [482o F]
This is much less that other materials tested, however, none of the other materials are used at baking temperatures.
Another study Regarding the Evolution of Formaldehyde from Polydimethylsiloxanes states that OSHA’s hazard communication requirements apply to formaldehyde releases greater than 0.1 percent. GE Silicones elected to include formaldehyde warning statements on some of their silicone products that might be subject to conditions under which formaldehyde might be generated to this level.
Here are their results for silicone testing:
They concluded “there is very little formaldehyde evolved until about 200°C (392°F).” This may be where my reader got this number.
Once again I am prompted to say that the problem we have as consumers is we don’t know exactly what type of “silicone” is used in any “silicone” product.
But it’s highly unlikely that formaldehyde would be released from silicone cookware or baking mats if you were to use them for baking cakes or cookies at 350 degrees F. There would be zero formaldehyde release if you used silicone forms to make ice cream bars or popsicles.
We don’t even know if a silicone baking form or silicone baking mats are even the “methyl” type that releases formaldehyde. This research was done on industrial silicones used at high temperatures.
Given this information, I would say it would be prudent to not use silicone for baking above 300-350 degrees F. But it’s probably fine for most baking below 400 degrees F.
Hi Debra I was wondering about my Breville IQ glass variable temperature electric water kettle which has a thin silicone seal where the glass meets the metal on the bottom. I know metal can leach but what about the silicone? Considering this new found information, do you think this in unsafe since it boils water along with the silicone? Thanks!
Water boils at 212 degrees, which is below the 300 degree threshold. So it seems like it would be OK.
I use a flat clay baking dish for roasting vegetables. I also use pyrex glassware at high temperatures and have never had any issues. Stay away from Silicone, metals, aluminum, and plastics. There is not enough “transparent” information and the chemical companies have complete disregard for our well being.
I agree about the pyrex glassware, but just be wary of heavy metals in clay. Xtrema is fine but just any clay cookware or bakeware could be contaminated with toxic metals.
As you know, I feel fine using silicone baking mats and silicone-coated parchment paper. I think it’s better than putting food on metal.
But I actually am moving away from almost all foods I used to cook in the oven. Only still roasted vegetables, which I cook in glass bakeware from IKEA.
Hi Debra,
What exactly do you mean when you said you are actually moving away from almost all foods you used to cook in the oven? I bake a lot for my family like bread and pastry. Is it not safe to bake? I only use USA Pan for all my baking and Xtrema. Thank you very much in advance for clearing this up for me.
Sincerely,
Alexis
I’m moving away from things like cakes and cookies and breads. Not because it’s unsafe to cook in the oven, but for other reasons.
Beyond Gourmet makes a parchment paper that is free of non stick coatings. However, it is made from 100% recycled paper and I wonder if this is safe for food as well? What do you think Debra 🙂
Actually, I use this exact parchment paper myself and I’m looking at the box and the parchment paper is NOT made from recycled paper. The BOX is made from recycled paper.
The parchment paper is made from unbleached paper with a silicone finish.
Hi Debra,
Which parchment paper do you feel safe using for baking? And what temperature do you recommend using this particular parchment paper.
Thank you very much.
Alexis
I use If You Care Unbleached Parchment Paper. And I use it up to 425 degrees. I don’t use it very often any more just because I don’t often eat foods like cookies that require baking.
Hi, Debra! By the way, the parchment paper I have seen has a silicone coating. Do you know what a typical parchment paper coating is made of? Thanks!
Silicone.
Hi Debra,
I just ordered two USA Pans sheet pans with the silicone coating. I intend to roast vegetables, which require a temperature of 450 (the limit of temperature of the pan, as you know). What pan should I use at the 450 degree temperature, if not the USA Pan?
I roast vegetables at lower temperatures, like 400 degrees.
I have, from many years ago, aluminum-steel baking sheets “half-sheet pans” and I just put parchments paper on them, which again, has silicone. But it’s either silicone or metal, and I prefer silicone. Or don’t roast your vegetables.
You can also use glass bakeware.
Debra, I do as you do. Just one clarification, though… My understanding is that the glass bakeware shouldn’t be used at those higher temperatures, correct? I think I’ve read not to use it above 350 or so.
I don’t have any data about not using glass at high temperatures.
what about silicone bags for sous vide cooking methods (immersion circulators or water ovens?)
Boiling water is 212 degrees so sous vide cooking should not release formaldehyde from the bag.
How does this apply to glass containers with silicone lids in the microwave?
Silicone would be fine in a microwave, as the temperature rarely exceeds 212 degrees F.
I have a professional grade formaldehyde monitor in my living room, about 15 feet away from my kitchen. I have been puzzling why often when I cook the formaldehyde level in my homes goes from 0.00 ppm (parts per million) to “unsafe” (above 0.08ppm) of formaldehyde. It doesn’t always happen when I cook but it does happen often. Lately it has been happening consistently and lately I have been cooking on my Silpat silcone baking mat. I roast vegetables at 350 F for 30 minutes. The other night it took hours before my monitor showed the formaldehyde levels to be back to safe levels and finally back to 0.00 ppm. It was cold out so I did not want to turn off the heat and open windows.
Interesting. Thanks for the data. 🙂
I want to take back my previous comment from Jan 12, 2017. I have been doing additional research to determine if it is the Silpat baking mat that is causing my formaldehyde meter to go off. I spoke to a couple of scientists I know from Berkeley Lab who are do the studies on indoor air quality and the various monitors available. We have concluded that in all probability what I have been cooking / baking is creating ethanol, a VOC, and possibly some other VOCs that are confusing the electro-chemical sensor in my formaldehyde meter. I have come to learn that a by-product of bread baking is ethanol. Here is a link to Berkley Lab indoor air quality page which has lots of good information from the studies they have been doing. http://indoorair.lbl.gov/ They are currently completing a study on the various consumer grade “low-cost” home indoor air quality monitors like the ones Home Labs is using. The preliminary results are very interesting. The study should be published sometime this year.
Thanks for the updated info. I agree LBL is a great source of information on indoor air pollution.