Fit
The most important difference between men's and women's snowboard boots is the fit. First, women's feet tend to be narrower than men's, especially in the heel. Thus, women's boots fit tighter around the heel and mid-foot to keep the foot secure and stable in the boot. This reduces heel-lift and allows women to better transfer their energy from their foot through the boot and to the board. The second difference in fit between men's and women's boots is cuff height. Women's calves sit lower than men's, so women's boots are designed with a lower cuff than men's. When women wear men's boots, they typically find that the cuff digs into the middle of the calf, which causes pain.
Flex
Boot flex also tends to differ between men's and women's snowboard boots. Most women's boots have a soft to medium flex so female riders can properly flex their ankles in the boot. However, if boots are too soft, it's possible to lose control due to too much flexion of the ankle. More advanced riders or competitive snowboarders need a stiffer boot to absorb the increased pressure they put on the boot. Since male riders are often more aggressive than women, they typically wear a boot with a stiffer flex.
Boots and Bindings
Because women's boots are designed to be narrower than men's, fitting boots into bindings can also be an issue. It's important to pair boots and bindings of the same gender, as a men's boot may not fit into a women's binding and a women's boot may be too narrow to fit securely into a men's.
Style
The last difference between men's and women's snowboard boots is the color and design of the boot's shell. Many women's boots are made to look pretty, covered with bright colors or intricate designs. Although this addition has no functional purpose, it still provides a palpable difference between men's and women's boots.