After leather, snake skins are the most common material from which cowboy boots are made. Snakeskin boots usually have the skin only on the foot of the boot, while the shaft is made of leather. Since most guys wear pants or jeans over boots, all you can see is the foot anyway, so it doesn't matter that the snakeskin is on the shaft of the boot anyway. Most of the time, “snakes” will have the skin only on the foot and on inlays on boot pulls.
There are two different “cuts” of snake skin use for cowboy boots. “Belly cut” means that the skin is cut from the softer, smoother, underside of the snake. The pattern of the snake's scale coloring is often more pronounced and visible. “Back cut” means that the skin is cut from the back of the snake. The scales of the snake's skin are usually rougher on the back, and offer a striking appearance. In both cases (belly or back-cut), the skin is dyed, and a variety of colors are avaiable.
Because it is important to try to get one full snake skin on the foot of a boot, usually only large snakes are used: cobra, python, or rattlesnake. Interestingly, a market never really developed for snakeskin boots made of boa constrictors, which are very large snakes, too. (It is possible to find boa-skin boots, but they are not as plentiful as python.) Snakes whose skin is used for boots are “farmed,” much like cows are farmed for their meat and hides.