For this project you will need:
A sewing machine (but any kind will do--just a straight stitch--nothing fancy)
cotton fabric and coordinating thread
A sharp scissors (and/or a rotary cutter)
a measuring tape
water absorbing crystals
I started by picking some fabrics out of my stash, but you could buy a yard at the fabric store and make 9 neck coolers with it. I cut my fabric 4 inches the whole width of the fabric (usually 45 inches). If you were making coolers for someone who's petite or for kids, you probably wouldn't need to cut them as long. You should prewash your fabric before you make your neck coolers. The fabric gets softer, and you won't have to worry about possible color bleeding.
I used my rotary cutter to cut several strips of fabric (I mean if I'm going to be dragging out the sewing machine, I might as well make a bunch). You could easily mark off four inches with a ruler and cut with a regular scissors.
After your strips are cut (and washed), fold them in half so the top is on the inside and the back is showing. I ironed them so that I wouldn't have to bother with pins for this step. Then go ahead and sew a straight line along the open edge. I used the tightest straight stitch on my little simple sewing machine (it's like the kind you buy for a preteen to learn to sew on--it's about as simple as it gets). Then use the presser foot as your guide for the seam allowance. Then comes the most tedious and hardest part of this whole project--turning those tubes back out to the right side. I don't own a Loop Turner (I have a tiny sewing machine--so I don't have all the fancy tools), but I hear those help a bit. I turned a couple of them while watching TV, and set forth for the next step. [Update! Hubby helped figure out a good way to turn these inside out using a dowel and a push pin. Check it out here.]
Fold your tube in half. Mark it with a pin. Then top stitch a straight line in that spot. I went over each line twice to make it good and durable. Then unfold your tube (that now has a stitch in the center, and pour 1/4 tsp of Water Crystals down one of the sides of the tubes. It doesn't seem like much, but they expand to fill it--I promise, you don't need more. Which means that I could make a gazillion of these coolers with that bag of water crystals (which isn't that big--remember, tiny sewing machine).
Note: Different brands of crystals may expand differently. If you're using something other than Miracle Gro crystals to make these coolers, you may want to do a test with a quarter teaspoon to see how much they expand.
Shake your crystals down so they are all situated next to the line you stitched. Then measure 4 inches and stitch another line. Pour another 1/4 tsp down the tube, shake, and measure 4 inches and stitch that section closed. Then move to the other side and repeat. You end up with 4-4 inch sections stitched into your tube--each with 1/4 tsp of water crystals (so 1 tsp for the whole neck cooler).
These sections help the neck cooler to bend and keep the crystals from clumping up in areas. You may want to adjust the size of the sections a bit if you're making a smaller one for kids.
This photo below is of a 36 inch neck cooler I made from a fat quarter (cut two 4 inch pieces the width of the quarter and sew them together to make a 36 inch long cooler). The contrasting thread makes it a bit easier to see the 4-4inch sections sewn into the cooler (click the image to make it larger).
Then when you're all finished with the crystals and the sections, tuck the ends of your tube in and top stitch them to finish the neck cooler off. I did the blue one below at an angle and the starry printed one in a straight line. I like the angled finish better and will probably use it for the rest of my neck coolers.
They don't look like much when they are dry--which means they are super easy to store in a camper or drawer at home. Then when you need them, toss them in a sink or bowl filled with water.
After ten minutes they looked like the photo below--and they continued to plump after that (see photo at the bottom of post). So allow atleast 20 minutes of soaking time for full effect. Then toss them in a zip top bag in your cooler or fridge to cool them off even more.
With the investment of a $7.99 bag of water crystals, I can make neck coolers for everyone I know and still have some crystals left for my potted plants. :)
Update: We wore our first batch while doing yard work and they worked fantastically! They stayed cool for hours, and they stay plump for days! It amazingly took about 10 days before they dried out enough to be stored flat again.
Update 2015: I'm still using the same set pictured, they dry out and replump with a soaking like the first day we used them.