> wrap that in aluminium foil, making sure that the ends are folded over and pressed down hard to provide good inter-layer contact

I've tried this many times, it's impossible to prevent gaps without welding it shut. Obviously I wasn't testing with an EMP or nuke, but trying to block 2.4GHz WiFi... But that is well within the E1 range the author states.

I think the problem with folding is it's too uniform, it's still too easy for waves to propagate through the humanly imperceptible gaps with only a few reflections.

The only method I found that worked consistently was to wrap many layers randomly overlapping and crumpling previous layers. My theory as to why this works is through self interference due to creating a long signal path with highly randomised reflections... No idea if that would help cancel out EMP.