The Dynarex Oxygen Tubing is available in two different styles, the Standard Lumen and the No Crush Lumen. The Oxygen Tubing with Standard Lumen has a smooth internal bore and measures 7-feet in length. The Oxygen Tubing with No Crush Lumen features a star-shaped interior cross section, reducing the likelihood of interrupting the flow of oxygen and measures 25-feet in length. Standard lumen has a smooth internal bore. No Crush lumen has a star-shaped interior cross-section which reduces the likelihood of interruption of oxygen flow.