EDIT: Featured on the instructables and lifehacker homepage, awesome! Just to clear some things up, the evaporative cooling doesn't work in humid environments but you can still use ice packs. And it's probably not as effective as just pouring water directly on your dog, but you will get the same effect without actually wetting your dog (and the wet dog smell), but anyways enjoy!
Need to keep your pooch cool for long walks on hot sunny days? Well look no further for this multipurpose vest will fit the bill (and your dog)!
The basic premise for the "cooling" part is you soak the the upper layer and as it evaporates it will draw heat from the lower layer with a waterproof layer in between to keep your dog dry. And also since it has side pockets you could throw some ice cubes in there too which will melt and then evaporate. Or you could just put flexible freezer gel pads or what not in there (or bags of frozen peas for that matter).
Old worn out cargo pants
Pins (safety or otherwise)
Step 1: Cut Out Inside Seam
Cut out the inside seam as indicated in the picture.
Step 2: Cut Out Main Shapes
After cutting out the inside seam, open it up, lay out the pant legs and cut out the shapes as in the picture.
Sorry I didn't take an pictures earlier, I tried to put together this picture in the later stages, but the basic shapes are similar.
You should have two cargo pocket pieces and one pant leg piece. The other pant leg and the rest of the pants aren't used (except for scraps for the fasteners later).
Step 3: Hem Edges
Now fold in about 3/8" on all edges and iron flat the lower layer piece, which will make it easier to hem. Then simply use a straight stitch about 1/4 " from the edge all the way around. You could do a proper hem folding it in twice so it won't fray so easily, but I was lazy.
Step 4: Add Fasteners
Next we add the straps and fasteners, I chose buttons since this particular pair of pants had lots of spare buttons that I could salvage. But you are free to use any sort of fastener (clasps, clips or buckles) as you wish, just try to avoid velcro (as suggested by criggie since they get filled with fur after a month or so)
These 3 locations should be enough to help keep the vest in place.
At this point you may want to try it on your dog to see how long you need to make the straps. Sew the straps to the main section and add the buttons and buttonholes as needed.
Step 5: Make Upper Layer / Pocket Layer
To make the upper layer, attach the two pocket pieces together and hem all around the edges on this layer too.
Step 6: Sew Together
Now we attach the upper and lower layers by simply sewing around, but be sure to leave one side open so we can insert/remove the waterproof layer
Step 7: Insert Waterproof Layer
Now find a plastic bag around this size or just cut one to size and insert into in between the layers. Don't worry about breath-ability since dogs don't sweat through their skin like us humans, they only sweat through their paws. In essence this vest will help them cool down by "sweating" the water that we soak the upper layer with.
I guess since we have the waterproof layer this may act as a doggy raincoat as well to some extent. Bonus!
UPDATE: You can also add another layer of fabric on top of the bag for extra water capacity or a thin spongy foam (like mattress topper) to help soak in more water as well so you don't have to re-drench it as often on really hot dry days.
Step 8: Attach to Dog
Now go put it on your dog, pour some water on it and go out for a long walk!