You probably mean resistance is very high (inf) instead of zero.
These thinks cant' be measured with a standard DMM.
They need something similar to an insulation tester, which outputs a high voltage (500V or 1000V) and meaures curren then.
These mats act a bit similar to a varistor, and they do not conduct current at low voltages.
You can try using a piezo electic spark generator (such as in a regular lighter) on it.
But I haven't tried that. Keep electronics away from such a thing though.