its expansion joint stuff, came on a roll from bunnings for about $20 to do both kegs with a little left over. The tape is holding it on and in place which is $20 per 50m also and a waste of money, any tape would be fine. its 'air cell insulating tape' paid for the name and didnt realise it wouldnt insulate by itself but jsu tseal it which is good i spode but any tape will do the same thing (maybe not look as good though?)
look at the top of this page and in the previous one there is a bit more info on it