It seems in the not-too-distant future the physical impression will become obsolete.
An in ear scanner will create a digital representation that can be emailed to a lab. It will then be manipulated, modeled and printed by stereolithography(SLA)resulting in a finished earpiece. Some labs are already receiving SLA scans.
In the future, just as we are amazed plaster of paris was used in clients ears, someone will be surprised that silicone was actually used to inject into our clients ears