Friction feed paper folders use rollers to pull sheets of paper in for folding and are the most common type of folder. While air feeders use bursts of air to push sheets in, friction feeding achieves fast speed with a rubber coated roller that uses friction for grip. Most light and medium duty folders use friction feeding, ideal for those personal desktop models. Air feed folders should be used for glossy stock and digitally printed stock as friction feed folders have a difficult time gripping slick surfaces. But for regular letter applications, a friction fed folder is the economical choice. While air-fed folders are typically bigger floor models, friction feed paper folders are available in different desktop sizes.