Impressions should be done by a qualified audiologist. This is perhaps the most important process for me to build you proper fitting monitors. With the jaw open and relaxed (I prefer no bite block), the impression material should fill the entire ear with no voids. A deep, second bend canal impression is necessary for proper fit, retention, and for minimization of the occlusion effect. It is recommended your audiologist show you the impressions once complete so you are confident they are done properly. A full helix is a must for proper retention, and good build up of material on the outer bowl of the ear is essential to create room for drivers and circuitry.