Not an ad for ReSound but perhaps anyone having custom molds made might be interested in ReSound’s recipe for getting a suitable impression from which to make a good mold.
RESOUND TRUFIT IMPRESSION
October 25, 2017
THE 16/4 RULE.
https://resoundconnect.com/blogs/gn-hear-and-now/impressions-article
There is also an Audiology Online course (which anyone can take for free) that shows how impressions are made in a video and reviews the 16:4 rule and good and bad impressions (requires a browser running Adobe Flash, which Microsoft browsers still permit on a case-by-case basis with user approval):
Dr. Cliff has a YouTube video praising the properties of Phonak custom earmolds (sponsored by Phonak!).