I was told by Costco in Sept. 2021 that custom ear molds are ordered from Westone (but at least at my store can not be ordered from Phonak). Westone as Mfg specializes in making molds and doess for many brands, however my focus is on KS10/Phonak. I have no affiliation with Westone or Costco.
If person through whom you are getting molds is very experienced/knowledgeable then below is probably not relevant to you.
OtoBlast is their silicone material option (see https://www.westone.com/store/hearing_health_care/earpiece-materials-and-colors)
This material additive is option that I might do: " e-Compound Additive
“e-Compound canal additive is designed to reduce feedback by diffusing reflected sound between the tip of the earpiece and the eardrum. e-Compound is available for all standard acrylic earpieces and can also be ordered in combination with the flex canal option.”
This finish option (rather than Matte, or Gloss) SlickSil is one I want:
" Slick-Sil® AM (Anti-Microbial) or silicone earpieces that is proven to be 99.9% effective* against bacteria, germs and other pathogens. As a result, Slick-Sil AM can be part of an aggressive infection control protocol. Slick-Sil AM produces a beautiful velvet finish that not only looks great but also helps with the insertion of silicone earpieces by providing a low friction surface finish. *Independent testing performed October 23, 2009 in compliance with JIS Z 2801 standards."
I do not know if there is additional cost for either of these options.
Acrylic material is also offered
In addition to the e-compound material additive noted above, the following can also be added …
Flex Canal
“Flex Canal is a body temperature-reactive, semisoft canal additive available on all standard Westone acrylic earpieces. The unique properties of this material allow the canal portion of the earpiece to remain firm at room temperature for ease of insertion and then soften at body temperature for increased comfort and seal. The flex canal option is also available in combination with the e-Compound canal option.”
Vent sizes
4 different sizes (1.0, 1.6, 2.0, & 2.4mm) are noted on Westone order form.
HOWEVER my understanding of Dr. Cliff’s rule of thumb vent size recommendation {https://drcliffaud.com/videos/why-ear-mold-vent-size-matters} based on amount of DB loss is that for my audiogram a >2.4mm vent would be better, namely 3.5mm. Via Westone the only way I see to get larger vent size is to order molds with their SAV (Select-a-Vent) option {https://www.westone.com/store/hearing_health_care/select-a-vent-sav} which would have a maximum of 3.18mm.
Note that the maximum vent size that can be made for a mold depends on the ear impression and the overall diameter of mold as a limiting factor. Westone offers various styles/shapes of molds {https://www.westone.com/store/hearing_health_care/ric-rite-crt-earpieces}, and from what I see it seems that style 89 for Silicone offers the most real estate to accommodate a larger vent.
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I am not a hearing professional, but prefer to be a knowledgeable consumer. I often find that professionals do not have the time to know about options that are available. While I will welcome the input and experience of Costco fitter who I will see tomorrow, I also want to know what is possible. I did call Westone directly and was able to confirm that a provider can pay a bit more for quicker than first class mail shipping, they were reluctant to talk to me about anything else once they knew I was not a provider. They indicated that it is typically 3-biz days from their receipt of order and ear impression to their giving the mold to the shipping vendor for return. Depending on where you live 14 calendar days might be cutting it tight if that is the interval you have between Costco testing appt. and pick up fitting of aids and molds. Definitely want the REM done with your new molds.
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1st edit 9.30.21 to add: Commenter on this thread indicated that molds ordered via their Costco were from Phonak, so I conclude that each Costco HA dept is different with some only ordering from Westone (my Costco), some ordering from Phonak; and perhaps some using both or even another generic Mfg. I’d add that forum members have had success/preferred vent size that is significantly different from what the research articles suggest (and what Dr. Cliff summarizes as rule of thumb for vent size in a single chart).