What is the wadding used to wrap round the heater block?

Hi all,

As the title suggest what is the wadding that is used to wrap around the heater block on the CTC 3D printers? I ordered 2 new replacement 0.4mm nozzles and I accidentally tore the wadding for one of them. I can just put it on and use Kapton tape to hold it together, but it got me thinking what is this stuff made from? and can I just buy it from somewhere and make my own?

Can anyone advise?

Thanks