Test 1
The pots are thermally lined so we needed to see how long they kept things hot on their own.
After 3 hours boiled water in the largest pot had dropped to 63deg C.
Test 2
With a pillow on top boiling water dropped to 76deg in the 3 hours I left it another 3hrs & we were at 63degees - so better but still some improvement possible.
Test 3
I left it over night & the boiling water had fallen to 56deg after 10hrs.
Test 4
I decide to give it a go with some food to see how we got on. It turned out that the smallest pan was the perfect size for two portions of curry. This did mean the hole in my insulation was the wrong size so I opted to nest the small one inside the other two...thinking about it now probably not the best way of doing it...but anyway I got the curry going on the hob & put it in the haybox at about 10:30am. Starting temp in the saucepan was 99deg.
By 6:30pm it had cooled to 51deg but as we wanted to tip ít back in a saucepan, add some cream & bring it back to the boil that wasn't a big issue. The curry was quite yummy & well cooked, & served up with rice cooked in the yogurt maker was a very low energy meal.
Still a bit more working out to do but not bad as a trial version!