what material reflects microwave?

Metal, or just about anything that's metalized. Aluminized mylar would certainly count as a "simple film", and is somewhat conformal if you don't mind cussing a bit.

If you can't find it anywhere else find a hobby shop that caters to model airplane builders and ask for metallic Monocoat, or check out the hobby websites (Tower Hobbies is good).

You can also get aluminum backed duct tape (you _don't_ want 'regular' silver-colored duct tape -- you want the stuff that looks like aluminum foil).

Or you could make a form, spray 3M 77 contact cement on it, and apply aluminum foil.

Come to think of it, even something like silver paint might -- although if it did it'd probably scatter quite a bit.

The material that is embedded in some microwave popcorn bags (which is why they always say "This Side Down". Ditto for some microwave frozen dinner entres.

-mpm

Anything metallic.

Those things are designed to absorb, not reflect.

John

Maybe for frozen dinners, but I'm pretty sure the popcorn bag variety reflects? I'm trying to remember the "technical" name for it..... Getting old is a bitch.

...

Actually, that stuff (called "reluctor") doesn't _reflect_ the microwaves - aluminum foil does that admirably (I saw a photo shoot in an early microwave oven cookbook - they wrapped an ice cube in foil, set it in the oven next to a cup of water, boiled the water and the ice cube was virtually untouched.) But that stuff on the bottom of the popcorn pack is designed to _absorb_ the microwaves and turn them into just plain ol' heat. Sometimes you get those "hot pocket" thingies with reluctor wrapped around them to brown the crust.

I have a suspicion that the reluctor stuff is somehow related to "radar-absorbent materal" paint for stealth aircraft. ;-)

Cheers! Rich

No, John, they're designed _exactly_ to heat the packaging (hence the "this side down" admonition) and cause the heat generated there to heat the food by conduction, thus popping the corn on the bottom or browning the crust of a hot pocket thingie.

I suppose popcorn in a microwave _without_ the reluctor on the bottom of the pack would pop eventually, but it'd probably burn the corn before the rest of it pops.

Who wants to volunteer to do this experiment? Take a microwave bag, dump the corn out into a (microwave-safe!) plastic plate, dump some plain ordinary popcorn on another (microwave-safe) plastic plate, and start them up?

Please report back with results.

Oh, wait - you'd need two ovens. Or a stopwatch! ;-)

Thanks! Rich

The "Emergency Space Blankets" beloved by rescue and emergency services are aluminized mylar and cost something like one or two dollars per square yard.

Popcorn contains too little water (about 10%) to effectively absorb microwaves. Hence the "this side down" panel absorbs microwave energy and heats up.

Of course! Why didn't I think of that?

(please don't answer).

is

Maybe "susceptor" is the right term I was thinking about, but it doesn't ring a bell. To the OP, US Patent # 6,559,430 is worth a look.

I of course, could not resist the temptation to do a patent search on "Inventor =3D Orville Redenbacher". Boy was I disappointed. :)

How about single side PC board material? The real thin stuff, 0.008 inch FR4 with 1 Oz copper is cheap. Check ebay.

tm

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A conductor, or a material with high magnetic susceptibility, will block radiation.

There are aluminized films, of course (but beware, the long wavelengths you are referring to will tunnel through a very thin film). Construction materials like aluminized foam insulation have thick-enough metal, and there are nickel-containing conductive paints that do a DANDY job, they both have conductivity and susceptibility on their side.

Seams must be made conductive, too, of course (there's a line of

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household aluminum foil

glue aluminum foil to your plastic sheet;use 3M spray adhesive.

Aluminum foil. Preferably hat-shaped.

I have lots of time, but little money on hand.

Radio amateur often make boxes for subassemblies by cutting double sided PCB boards into suitable plates and soldering these plates into a box, with slightly overlapping sides. These boxes are mechanically stable and good EMC isolation, so that small signal subassembly units can be close to high RF power (10-1000 W) subassemblies.