Mash tun insulation

I am almost ready to convert my old kettle/HLT pot into a mash tun, just waiting on bulkheads to convert my second keg into the new kettle then I can say good bye to the old rectangular chilly bin mash tun.

I'm thinking about insulation and although finding a bigger vessel to put the mash tun inside and filling the gap with expanding foam would be my preferred option every thing I can think of for the outer vessel is expensive and/or ugly and/or really heavy. So now I'm thinking yoga mat.

How good is the insulation you get from wrapping a pot in a yoga mat?

What do people use to stick the mat to their pots? I'm thinking maybe liquid nails, obviously it has to not melt in the heat.

I might put some wood on top of the yoga mat at some stage If it doesn't look like adding too much weight.

Any suggestions for alternatives welcome. Its a 50L pot 400mm diameter and about 400mm tall.