The XL sizes are 5 inches longer than regular sizes, they are meant for taller people.
Twin XL beds, or extra long twin beds, are commonly found in college dorms and hospitals. These beds have the same width as a regular twin size bed only they provide 5 extra inches of length measuring 39" x 80". Full XL mattresses have the same width as a regular full-size mattress but have 5 extra inches in length measuring 54" x 80".