Eco-Cooking - Wonderbag.

Had a quick look - do you think they work on the old straw box principle? Very snazzy web site with grand claims but perhaps someone has tried them and can let us know as you say Butternut

Yes. Very similar to the old straw-box system.

yes it must be the hay box principle. Heat stew to boiling point and put it in an insulating jacket for several hours to slow cook.
I suppose it is a bag filled with polystyrene granules.
Is it any more efficient that heating your casserole to boiling point and then turning off the oven I wonder? Most modern ovens very well insulated and keep things hot for a long time. And you use the heat left in the oven after the power turned off.
I can see that for people in 3rd world who are cooking on fires/stoves that this might be a really useful item. Esp if they mainly eat stewy things or grains and pulses that need long cooking. When i used hay box in guides we used it overnight.
I only do stewy things rarely and then probably in one big batch and use the turning off the oven trick as above. So this would not be the gadget for me.

Took delivery of my Wonderbag at the weekend and made a beef rib trim casserole which I put in the bag at 11.30 am and took it out to dish up at 6.30pm. The pot was still hot that I had to use oven gloves! It was delicious! The meat was cooked lovely but didn't break up and the veg had not gone sloppy after 7 hours! It's great if you want to go out for the day but don't want to leave a cooker on. There are lots of recipes for it and it can also be used to keep things cold (frozen chicken pieces will stay that way for 12 hours) so great if you are self catering. One of the other nice things about it is the fact that because I bought mine a free one will be given to a family in Africa. I hope they enjoy it as much as I think I will mine.