I have been working on this and trying to track down beans to fill it. I was told to look for local craft shops but there are none that I could find in my area. I managed to buy some online at http://www.beanbagrefill.com in case anyone else has the same problem.
We are working on making Wonderboxes as a group. I am experimenting before we have everyone start. I have made mine and filled with polystyrene beads double the size of a kidney bean manufactured to fill a bean bag chair. My friend used tinier beads and they seem to work better. I am having problems finding this tinier size. Does the size make a huge difference? Ideas on where to find the tiner size? Craft stores have not panned out.
I believe the smaller beads will have a better insulating ability because they will better be able to trap the air and heat between the beads and prevent the heat from radiating or convecting outward. The larger air pockets left when using larger beads gives the heat more avenues to transfer the heat outward. Air is a very poor conductor of heat so minimizing the empty air space around the beads will give you much better insulating performance. In short, smaller beads equals smaller empty air pockets which leads to better insulation performance.
I wonder, could you use something else? I have a “corn sack” it is filled dry corn and you throw it in the microwave for a couple of minutes and it stays hot for a while. I wonder if something like this would work?
I ordered beads at studiooneup.com. The beads are tiny, 2 to 3 mm each. It took 1 and one-half pounds of beads to fill the top and bottom of my wonderbox (12 gallons in the bottom, 7 gallons for the top). HTH.