Rubber doesn't shield. To shield electronics you have to use a "Faraday cage". For an example of one, see "Enemy of the State". Basically it is a grounded wire mesh or box that completely surrounds whatever electronics you are trying to protect. You can have NO wires or antennae out of the box or it will pick up the pulse and channel the signal into your electronics. The whole reason EMPs are so worrisom is that the ElectroMagnetic Pulse theoretically will be picked up by ANY wire (all wires will act like antennae) and funneled through the more delecate ones. It is theoretically possible that more robust wiring will survive but any small wires (transistors, light bulbs, LEDs, computer chips, etc.) will probably overload and burn out. The two ways to shield are either to design the electronics to make it cancel itself out (hardening. My father worked on it over at Naval Ordinance back in the 60s), or put a faraday cage around it to channel the pulse to ground before it gets to your devices.