Making beef jerky. You lay the strips of beef in the creases of the furnace filters, then stack the filters over a box fan and strap em down. After seeing Alton Brown do it, I thought I would give it a shot. The results were mediocre. The cut of meat wasn't as lean as I wanted, so it was a little chewy. I think I used flank, so next time i'll use top round or something similar. I have a few issues with this method. First, the filters do not allow enough air to pass through them if your using a cheap box fan. A high powered fan might work better, but rather than those filters, I would use metal mesh or grating attached to 2x4s or other frame. I have seen that done elsewhere. Second, the filters tend to leave bits of fuzz attached to the meat. Not a lot and not a huge deal, just an annoyance. Thirdly, all told, I probably could have bought a cheap dehydrator for the same amount that I spent on the fan and the three filters. I couldn't find the two $ ones he was talking about. They are more like six. If you want to do the cold-dry box fan method, I would suggest the mesh or grates to the filters for better air circulation.