There are many different style caps - the most common are the full lace cap with ear to ear stretch, the full lace cap with no stretch, and front lace only cap meaning lace in the front only.
Ear to Ear Stretch - (highly recommended) It is best used as standard sizes small, medium and large.
No Stretch - The lace is constructed using 6 measurements giving by customer. Follow these instructions located here to get your personal six measurement are located here.
Glue less Cap - These are the newest style full lace wig cap available. Constructed with a strap in the back and elastic around the circumference adds to secures the wig while wearing.