Pouch Material

I have a decade of experience cutting, forming and shooting assorted types of leather pouches. Elk, moose, kangaroo, cow and pig. I don’t really shoot leather much anymore though. In my opinion synthetics are far superior.
Forget about the velocity difference. It doesn’t really exist and if it does it’s pretty much inconsequential. Unless you’re building some sort of large rock chucker setup then size just isn’t all that important.
I shoot synthetic pretty much exclusively these days.

There are several real good reasons for shooting synthetics aside from how robust synthetics are that few ever talk about and they all have to do with “cupping” the pouch and the shedding of the ball before it reaches the fork.
Leather has a “grain”. When cutting your own pouches it’s imperative to stretch the leather in various directions until you figure out in which direction it stretches most. When you do this you discover that when stretched with the grain the leather will form the beginnings of a pouch all by itself. Cut the leather along and in the same direction as the grain and ball will hold more securely during acceleration. Accentuate the natural pouching with wetting, stretching and forming the leather around a ball and letting it dry in place will help form the pouch form as well.
I would guess that 90% of my fork hits through the years have been because of the pouch shedding the ball during acceleration. Commercial leather pouches are generally made from two pieces of leather glued together while crossing grains. They tend to be flat, difficult to form a pouch in and subsequently a hole needs to be punched in the center in order to center and hold the ball. The hole can stretch in time which can, in turn, effect which size balls can be shot. (This happens very rarely with synthetic - though coincidentally it happened to me just today with a real thin synthetic and a 5/16 ball. Go figure.
The thicker synthetic pouches that you are speaking of do not stretch so there is no deformation to worry about. More importantly though is the ease with which they can be permanently and easily be formed into a pouch. Simply wrap the pouch tightly around a 5/16 ball and swirl a flame from a lighter around it quickly, form it a bit more with your fingers and you’re done. Five or six seconds and that’s it. Even a fairly narrow synthetic pouch will securely hold a 7/16 ball. I use the same technique on thinner and narrower pouches as well but flame it for only two or three seconds. I shoot up to 7/16 with these as well. Pretty much 0% shedding with the synthetics.