Tony, yes, that's what I am thinking. I thought of making the cozy 3/4th's the depth/height of the pot/cup. This would save weight and prevent it from catching fire if flames licked up the side on a flaring stove (if made from Reflextix).
Foil seems to require too much care to me in the field to be durable for the long haul; but I may be tougher than you on gear. Maybe a foil formed bowl, one already sold, would have thicker AL and be more durable? It could be trimmed/crushed down as needed to conform to the bowl.
That said, if the purpose of the cozy is to be 'heat retentive' then which material(s)work in this regard? Reflextix bubble wrap, HD AL foil, foam, neoprene; for the weight? Ahem, Mr Nisley,Bill F, anyone else with more specs' than i care to chime in here?
Cool stove in that first post's picture Tony! Nice flub!