[Florin_Andrei]

> I think they are magically 100% effective.

No, they are not. Even a continuous, zero-hole metallic bubble will leak some radiation inside, depending on frequency, nature of material, wall thickness, etc.

Start here:

https://en.wikipedia.org/wiki/Penetration_depth

then continue reading about absorbance, skin effect, etc.

[JoeAltmaier]

I see. Only for zero-resistance metal would skin depth be zero.

[JoeAltmaier]

At microwave frequencies, skin depth is essentially zero (microns anyway) for most metals. So until the bag is melted, nothing will get through.