Lead is for stopping what’s called ionizing radiation — Geiger counter stuff — like Alpha, beta, gamma/Xrays, not EMP, although it is a pretty good conductor, and you COULD fashion a proper Faraday cage to guard against EMP. But don’t. Use steel or aluminum.
EMP = electro-magnetic pulse = damage to electronics from induced current.
A poor man’s method to shield electronics is fairly simple and cheap.
(1) a metal box with a ‘lid’ that seals pretty well. An ammmo can is just about optimum. You want it sealed so the energy of the pulse cannot get through a gap bigger than the wavelength of the pulse.
(2) wrap the electronics to be protected in an insulating material to generate a space gap and an insulating shield from the box itself. DRY paper, multiple layers will work pretty well, and finish with bubble wrap on the outside of the paper. Add some silica gel or other dessicant to the can.
(3) Place the can on a grounded surface — like the garage or basement concrete floor. (3.1) for overkill - drive a copper rod into the ground and ground the can(s) of protected devices. (3.2) the idea is to keep the pulse and any induced current away from your stuff, and to provide an easy path to ground/earth for said current and pulse.
No need to build Faraday cages. Just ammo cans, paper and bubble wrap.
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So, basically the current travels through through the box to ground and not through what you’re trying to protect? Ok, then would it be a good idea to also line the inside of the box with a non-conducting material like rubber?