A 50/50 split means that one side of the holster will cover 50 % of the thickness of the gun and the other side will cover the remaining 50%. In other words, each half of the holster will cover half the thickness of the gun. The two pieces of the kydex will meet right down the middle of the slide. Now that we have discussed what it is, you have to talk about why you would want to do this. There is a strong misconception that a 50/50 split is preferable when making a holster. That is simply not true. Stuart proved in 2013 with the invention of the curved jig that an 80/20 split or a 90/10 split will make a much better, more comfortable holster.
Making a 50/50 split might be the cheapest way to make a holster but it certainly will not make the most comfortable holster. If making 50/50 holsters is what you intend to do on a regular basis, we strongly recommend using split molds that will speed up the process and give consistent results. But, you can easily make a 50/50 holster inside the vacuum former without split molds. Say for example you want to make a 50/50 split holster for a Glock 19. The slide on the G19 is about 1 inch thick. This means each kydex shell will need to be roughly 1/2 inch in height to work. So, take a piece of 1/2 inch neoprene foam, lay the G19 on the foam and cut out around the G19. You are making a foam recess for the G19 to sit down into that is 1/2 inch deep. Take another piece of half inch foam the same size and slide underneath the cutout you just made. Put all of this into your vacuum former. Lay the G19 into the recess. Form a piece of hot kydex over the top of the mold and allow it to cool. Pick up the G19 with the kydex shell. Flip the foam cutout over. Put the G19 and the shell back onto the top of the foam cut out. You should now see the kydex shell resting in the foam cutout with the G19 mold laying on top of it. Now form another piece of hot kydex on top. Now you have a 50/50 pancake holster. This process sounds complicated, but it is quick, easy, and cheap to do once you learn it. Use different thicknesses of neoprene foam to adjust the amount of the split or for thinner / thicker handguns. As a holster maker, you should always have different thicknesses of closed cell neoprene foam in your shop.