Jacket base is the bottom of a jacket, all the way around the entire jacket. It is usually made of a heavier fabric than the rest of the jacket, and it can be plain or decorated. The jacket base helps to keep the jacket in shape and provides a smooth finish. It can also be used to add insulation or decoration to the jacket.

The type of jacket base used will depend on the style and function of the jacket. For example, a plain hem is often used on a casual jacket, while a ribbed hem is more common on a sports jacket. A vented hem can be found on a hiking jacket or other jacket that needs to allow for a lot of movement. And a decorative hem can be used on a dress jacket or other jacket that is meant to be more stylish.