This is about amp feedback.
There are many opinions about how to eliminate amp feedback from your cigar box guitar, but I gotta say that I have found the best and easiest method is to line the entire inside surface of the box you're using to create your masterpiece with foil.
Now, some folks recommend copper foil tape (expensive) as the best and only real method. Others say aluminum foil tape is the ticket (expensive, too). Many also tell the story that the tape strips must be connected by the use of solder to be effective. All this sounded like overkill to me, so, after experimenting a bit, I discovered there is an easier way, less expensive, but dangerous if you are not the sole proprietor of your kitchen.
Reynolds aluminum foil is the deal. While your wife or significant other is away, sneak into the kitchen, grab the biggest roll of foil you can find, take off for the workshop, and you're ready to put the kibosh on amp feedback.
All you need in addition is a small jar of contact cement, scissors, mineral spirits (to clean the sticky crap off your fingers), a sharp knife to trim the foil to make it a real sanitary installation, and somewhere to hide the roll, when the kitchen help discovers it missing.
You're ready. Rip off a strip wide enough to fit the inside of the box. Coat the surface of the box to be covered with contact cement. Lay the foil (shiny side up) on the sticky surface, and smooth it out. Cut the corners with the knife to facilitate a good fit, and finish smoothing the small areas. Go all the way up the sides of the box with the foil as well, leaving a little foil to be rolled over onto the edge of the box (this ensures that the top and bottom of the box foil will make contact when the unit is put together. Cut away foil from pickup, tone/volume controls, and output jack to prevent careless grounding.
That's it! No numerous small strips of foil tape to screw around with. No solder (you're not trying to create an electric conductor, only a shield to prevent signal feedback from the amp to the guitar).
This method may not be what the big boys use to shield an instrument, but it works for me. And, just add a little clarity, I took my Strat apart to see what they do, and I was surprised to find the control cavity contained only a little piece of foil, apparently the solid body does a good job on its own to shield.