You are making the current version of a project I have made with a few of my students, and it hasn't even got hot yet to see if it works or maybe brings on a migraine! (Future versions might have ways of getting the air up and around the scalp using more distributed ducting.) You will need hot glue or something like e6000, a soldering iron and solder, a utility knife and a noodle nose pliers. You will need a computer fan that runs on 9V, a battery snap and optionally a switch (I used a small DPDT which I will explain as we go.) and either a battery clip which I used to run out to a CERTAIN electronic parts retailer and now must order online (not shown), or a small change purse or one of those free belt clips you get with small flashlights.

A word on the hat: it needs to be a baseball cap, because this will keep your hair down and away from the fan. A tennis visor is a no go for this reason. For safety, all your hair has to be down and away from the intake (upward) side of the fan. That said, ready?

Step 1: The Electric Cooling Hat

This hat has a computer cooling fan inserted into the brim to provide a welcome breeze on really hot days, right up along your hairline and across your forehead. You get to learn about electronic circuits and do a bit of soldering along the way. You'll need to be comfortable with utility knives, your hot glue gun and your soldering iron.

Step 2: Cutting the Hole

Trace the fan with a pen or marker. Using the utility knife and an abundance of caution slice through the three layers of your hat's brim: there will be the thin fabric top and bottom and either plastic or cardboard. You may wish to trim the frilly bits of the edge now with scissors, and it might take some careful trimming to get the fan to fit snuggly.

Step 3: Gluing in the Fan

Set the fan about halfway into the hole with the wires close to the forehead and with the label side down. WHY? These fans are usually attached atop a heat sink which is clipped to the heat-producing processor chips inside mainframe computers, and they draw air up through the sink pulling heat from the chip. Thus if you want cool air blowing on your forehead you want the label side down: that's the "output" side of the fan. Run a generous bead of hot glue around the rim of the fan on the top and bottom side of the brim. This will hold the fan in place and restore the stiffness to your hat and it will keep the fabric from pulling and fraying around the hole you cut in it.

Step 4: Run the Wiring Under the Brim

Using your utility knife and another abundance of caution slice a thin slit in the band through which you will push the two fan wires. Don't have long enough wires? Have the kind of fan with three wires? You will need to determine which two wires allow the fan to run off 9V and you may need to solder in some longer wires here. You want to be able to feed the wires around to the back of the hat and have something to work with back at the hat's size adjustor. Ideally, the wires should be red for positive and black for negative, although we all know that the color of the wire is just for your convenience. If you're a lifelong tinkerer as I am you have take-out food containers around the place with bits of wire in them. If not you will need to find some thin wire somewhere such as the fan already has...go ahead...we'll wait...

I used a tack of hot glue every inch or so to keep the wire in the crease of the band, and conveniently for me, as I got these fans off Amazon for the students to use, they had exactly as much wire as we needed.

Step 5: Why the DPDT Turned Out to Be a Good Switch to Use

This little toggle switch is two switches side-by-side. Looking at the bottom where the terminals stick out, think of each switch being the three little pins like needles with their eyes all in the same direction. So as in the first picture, choose any two in a row and put the red wire from the fan into one and the red wire from the battery snap into the next one along on that side. Notice that one wire is in the middle pin for that side of the switch; that's the "pole" in the switch's name. Thus when the toggle is "thrown" in the other direction there's a little ball bearing or nylon slider on a copper see-saw inside the switch that has flopped a conductor across those two pins and now it's "on". In the first image, in fact, the switch is "on" for those two red wires. Go ahead and solder them in place.

Step 6: Keeping the Wiring Neat

Two options present themselves. With the red wires now able to switch on and off, we only need the black wires touching for the fan to run. In the first image, we have "tied off the grounds": typically I'd wire the two black wires together and tape them off or hot glue them down or in a guitar I would use a little heat shrink tubing to be sure they don't wander around and short my circuit. So option one here is to tie off the black wires and find some place to glue them down. But we are using a DPDT switch, meaning we have a whole second set of pins with nothing to do. In the second image, we have simply used the parallel switch, or the other pole and the corresponding one of its two throws, to have the black wires also be switched on and off. Electrically redundant, but neater, I think.

Step 7: Holding the Battery and Switch

You have found a little pouch of some sort to hold your battery. Run two generous beads of hot glue along the back of this, and attach it to the back of the hat above the adjuster. Use hot glue to attach the switch to the under side of your battery pouch. I the hat in the picture, the hook'n'loop closure of the pouch keeps the battery and its wires neat and out of sight. The switch takes a little fumbling when you are wearing the hat, but with a little practice you can reach around and switch it on and off without difficulty.

If you are building the hat without the switch, simply take that battery snap off the battery to turn it off.

Step 8: Duct That Airflow!

Now we need to direct the airflow up to the hairline. Cut a flap of cardboard or any old non-porous fabric you have around; it's a bit of seat covering vinyl in the image. In the first image here you can see two small slits near what will be the back edge. In the second pic what will be the front edge has a bit of curve in it, so it doesn't hit the forehead. Run a bead of hot glue along the two side edges and glue down as in the third picture. Notice my thumb holding up the flap we cut earlier. The flap allows you to tuck a little more glue up in there -- not so much as to interfere with the fan blades! -- and get a good seal around the back of the fan. At 9V it is not pushing too much air, so we need a good seal around three sides of the flap. In addition to the curve we cut into its shape, so as to follow the contour of the head, we also need a bit of curve away from the brim in the open side so the air has someplace to go. The fourth pic here shows the hot glue seal at the back of the ducting flap as well as the outward curvature of the open side.

That's it; wear it and enjoy it on hot days! I'd not leave it on for too long at a time if you feel it's only blowing on one small part of your head or into your eyes.

Step 9: Enjoy!

Feel free to offer advise or adjustments. The wider an area of the forehead to which the air can be ducted the better, and up and under the hat and along the scalp wound be ideal.