Building the pad

The pad itself is really easy to build:

The basis is a mere foam mat (the one you use for hiking or for yoga)

Their size is usually around 180x50cm.

Cut it:

And the put the pieces together to have a square.

Now cut four pieces of A4-sized aluminium foil. Attach a small wire to each.

Put each piece between two transparent plastic sheets. Now put everything together with lots of adhesive tape. That’s it !