Dude, any COTTON sock will do, no pantihose or any other synthethic materials cause they get realm hot and will burn your skin off, well.. melt it off is more accurate.
Any rice will do, it's just there to absorb the micro wave radiation in the form of heat and let it out in a slow fashion due to it's properties ( density and radiative props. ).
Also, it is a choice done by pure common sense, it will 'deform' and adapt to your any body part but while still releasing the heat in a steady fashion.
So, get an old CLEAN sock ( for your sake lol ) and fill it up with any raw rice and nuke the bastard with a few secs antil hot enough to help but cold enough to keep from getting burned.
Peace
Mike