So this is a quick, quality fix to the question "What do I do with my keys while I run?"

What you'll need is:

Access to a laser cutter. It can be a smaller one, I made my band out of 8.5x11" PET sheets. If you don't own a small personal laser, check for a local maker space and see if they have one. If not, this is not 100% necessary but it does make the parts more clean, uniform and easy to assemble but hand cutting is still a valid option.

A few sheets of vinyl, silicon, PET Plastic, waterproof ripstop, or other waterproof material- Make sure with PET that it's no thicker than 0.02" otherwise it will be too rigid to accept your key. If you plan on laser cutting, make sure that the heat of the laser won't effect the waterproof qualities or coatings of your chose material.

You can use another waterproof fabric or plastic, just double check that they are safe to laser cut.

A seam sealer of some form - You can usually find an option at your local REI or outfitter. anywhere that sells tents should have a tent seam repair kit that will have the right stuff. These are two options you can use. https://www.rei.com/product/603034/gear-aid-seam-g..., https://www.onlinefabricstore.net/black-hot-melt-s...

A waterproof/weatherproof zipper - I found this one on amazon. You can just cut the tag end to the length you'll need and glue it in. https://smile.amazon.com/gp/product/B07D3S58SM/ref...

And lastly you'll need a slap bracelet. - I found a reflective, LED one at Walmart, but NiteIze also makes this one that is an option or you can buy a basic silicon one at your local hobby lobby or dollar store. These are simply just an old tape measure cut to length and coated in silicon/plasti-dip or sewn into a fabric. I have not tested making my own band so if you try this let me know how it goes in the comments below. https://www.amazon.com/Nite-Ize-Bracelet-Nighttime...

Supplies

Vinyl Sheet - https://www.amazon.com/ProMAG-Paintable-Magnetic-V...

A seam sealer of some form - https://www.rei.com/product/603034/gear-aid-seam-... https://www.onlinefabricstore.net/black-hot-melt-...

waterproof/weatherproof zipper - https://smile.amazon.com/gp/product/B07D3S58SM/re...

slap bracelet. - https://www.amazon.com/Nite-Ize-Bracelet-Nighttim...

The attached Files for the part template.

Step 1: Cut Your Parts

Once you've bought all your materials you'll want to use the attached 3D part file to edit if you need extra space, export a .dxf and laser cut your plastic. If you don't need to edit then you can just load the Adobe Illustrator file directly into the laser software to cut. If you're not laser cutting, then you can print out the PDF template to cut it out to trace for your hand cut lines. I built the laser template file in SolidWorks, but a free trial or educational version of Fusion 360 from Autodesk will allow you to open and edit the parts and dimensions as you need.

Step 2: Gluing the Zipper

Now that your parts are cut out, we can start assembling. Grab your zipper, seam sealer and the plastic piece with the largest cutout. I've found that if you have a few pop sickle sticks laying around they make this process a little easier.Trim your zipper to length and round the corners. Place your plastic face down on your work surface (if you have the pop sickle sticks, lay them 1-2 high on each side of the opening under the plastic). Now spread your seam sealer on the plastic and lay your zipper outside down on the glue (the pop sickle sticks compensate for the height of the zipper pull so that the zipper tape gets solid contact with the glue and plastic). If you're using the tape, then just lay your plastic face down with the zipper in the same orientation on top of the plastic and then tape the back of your zipper. Now flip it over and seal the top of the zipper without puting the seam tape down where it will obstruct the zipper pull.

Note: after your seam sealer has cured, you might have to flip it over and seal the topside of the seam. The key is to make sure that everything is adhered well and you have a complete seal.

Step 3: Gluing the Back Together

Grab your two remaining pieces of plastic and place the one with the inside cuts on the bottom (back down). You'll want to draw a line across the top and bottom edge of the cuts creating a box the height of the cutouts. You don't want any glue in this area since your strap has to pass through here. (I laid down some wax paper for the sealer application just to keep my work surface cleaner since you'll be dragging the brush and sealer off the edge of the pieces). Apply seam sealer everywhere else, make sure to spread it all the way to the edges, and place the last plastic piece on top and make sure there is solid glue contact. With seam tape just fold the tape over all the edges.

Step 4: Closing the Pouch

After you've let the glue on your two halves cure, spread about a 1/8th to 1/4" bead of seam sealer around the edge of the zipper half. Spread it to the edges of your piece using a brush (most repair kits you buy will have one in them). Place it on the other half of the plastic with the inside cutouts on the bottom so they are on what is the outside of the pouch. After this sealer has dried, go back around the edges with sealer and double seal the edge for extra water resistance. If you're using tape, just fold the tape over all the edges and you're ready to put your band through.

Step 5: Done!

After closing the pouch, just thread the slap band through the slots on the back. Start by going down from the top of the first side, then up, into the back of the pouch, down and out, and then back up through the other side slot. Now you're ready to go adventure without worrying about your key.