[kurthr]

If you're interested in simple cages similar in effectiveness to the EDEC Window Pouch (they drop off above 3GHz)... try a Microwave Oven. They are highly available, reasonably convenient and well designed, with pretty good quality control. You can even still see your phone inside has zero bars. I do, however, recommend unplugging the microwave (or even cutting the power cord) as a fire would likely result from cooking your hardware.

To answer [2] How big are the waves you're trying to block? - it's actually crack length not width that usually determines the effective re-radiating antenna length. They can be very narrow, but a long (a few cm) crack will allow one polarization through almost completely.

I've run this test with a GSM base station and confirmed the effectiveness. If you want to test communication with a device to a base station, but have many other local antennas interfering and want to fit many devices inside... it's a decent choice. The alternatives are less convenient and usually thousands of dollars to construct.

[Johnythree]

The door seals in most microwave ovens consist of tuned slots (eg half-wave stubs) to prevent the RF escaping. These are ineffective at frequencies other than 2.4Ghz.

The reason for the tuned slots is that it's basically impossible to make a conventional metal joint which will seal sufficiently well.

[kurthr]

I encourage you to test a few. I found that the cheap ones blocked 2.45GHz ~60dB, but that they were still down 40dB at 600MHz... the real problems were at higher frequencies and 5GHz was only down ~20-30dB at the worst case polarization. I tried using RF absorbing tape, but while it's possible to improve another 10-20dB it's painful and not repeatable without testing, if you need to remove it.

I've also worked in RF Antenna test rooms with seals that are expensive, finicky, and easy to damage... they're also at least $10k and usually much much more. In a corporate environment that's not a problem, but for a home lab it's unrealistic.

If these bags were big enough to put a few phones and a small base antenna in they'd have other uses.