Last week the power supply in my 55 inch television died.  Coincidentally, my brother had the same make and model, purchased at the same time, (independently, we live 500 miles apart.) and the power supply in his died the same week.  Now, while some people may find this evidence of quantum entanglement we found it an indication to not buy that brand again. (I won't post the name in the forum so as not to be sued but if you PM me.)  Anyway, I had to replace the television.

The new one arrived in a large, double walled cardboard box.  Faced with the task of getting the box into the recycling bin I began to cut it up.  I immediately realized that the double walled cardboard would make great building board material.  I liberated the smooth sides of the box and cut them up in half making four large building boards.  The remaining material easily fit in the bin.

This was a good find for me since I have multiple projects going at once and never seem to  have enough building boards.  If you are not using a magnetic building board and come across one of these double walled boxes don't waste the cardboard!