Even though this is food related I thought it was best here because it’s a general question…just happens to be about food.
As I am enjoying my high class breakfast of Hot Pock-ets! I finally started to wonder what the point of the little sleeve thingy that I have to use every time. I also noticed this with other microwave foods, they’ll have a sleeve or a little shelf (like with pizzas) and I’ve always wondered what exactly is the point of those? Does it help with the absorption of the radiation? Help it cook it more evenly? What’s the deal?
The radiation in a microwave is radio waves, which isn’t what people typically think of when you use the word “radiation” (they tend to think of things more like gamma rays). Radio waves are a form of electromagnetic radiation, so technically it is the correct term to use. There is no nuclear type radiation in a microwave though, so you don’t need to absorb radiation or anything like that.
The gray stuff on the inside of hot pocket cooking sleeves and microwave pizza box trays is a metal film. The radio waves from the microwave cause eddy currents to flow through the metal film, making it get hot. This browns the hot pocket or pizza (well, sort of, as Morgenstern said). Without the metal film, the outside of the hot pocket or the bottom of the pizza would remain doughy and chewy.
To get browning, you need to raise the temperature higher than the boiling point of water, which is pretty much the highest you’ll get with just the hot pocket. The metal, as noted above, gives you that extra heat.
Hint: before putting any metal-lined cooking assistant in there, wipe off any water, ice, or condensation you can. The dryer you can get it and the food product, the more crisping you can get.
You’re not supposed to discard it. You keep it within arm’s reach and then use it to direct the stream of vomit neatly to the nearest toilet or wastebasket.
Some look like foil-lined paper, so it’s obvious that they are metal. I’ve seen the ones that look like paint, I think it’s a metal-based paint with a sealant over the top to prevent it from flaking or rubbing off.
If you look at your local hardware store, they sell paint you can use to create a chalkboard-like surface for writing on. Newer versions include magnetic particles so that you can stick magnets to the chalkboard as well. I think it’s the same concept.
There’s nothing wrong with metal itself; microwaves themselves are made of metal; the problem is when you have thin sharp points which allow voltage to build up and cause arcs and/or heating, metal also reflects microwaves which could cause problems if they get reflected back to the magnetron (this can also happen if you run a microwave empty, since nothing will absorb the microwaves which will just keep on building up until they find some way to dissipate their energy).
