The Seatec chin straps was designed by a sleep technician who was frustrated by the chin straps available at that time. The purpose of a chin strap is to assist people with a nasal mask who also have mouth breathing and may want to prevent this from occurring. Many of the available chin straps are smaller and easier to remove throughout the night which means people sometimes take them off without realising.
Made by a wet suit company these have an elastic wetsuit type material which allows the skin to breathe.
The design has a Velcro attachment at the top that allows for adjustment to ensure the jaw is adequately supported throughout the night. The purpose of the chin strap is to support the jaw and should not be too tight that it is uncomfortable. the Velcro at the back allows for easy removal when getting up in the morning. These come in 3 sizes and the majority would be a medium.
Also available is the mouth and chin version which covers the whole mouth whilst supporting the jaw. These are very good when you have issues with lip leakage.