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Short answer: An earmold is a custom-made piece that connects a behind-the-ear hearing aid to the wearer’s ear. Earmold types are described along three separate axes: the style (how much of the outer ear it fills and whether it blocks the canal), the material (acrylic, vinyl, silicone, polyethylene and others, each with a different hardness and shrinkage behaviour) and the parts (sound bore, vent, canal lock, tubing method). This page sets them side by side, with each figure attributed to the audiology publication that reports it.
General product information only. It is not medical advice and does not describe how to take an ear impression or fit an earmold; those decisions belong to the audiologist or hearing care professional.
What an earmold is and what it has to do
Hearing Review’s “Anatomy of an Earmold” describes the earmold as an individually made component that must provide an acoustic seal, couple the hearing aid acoustically to the ear, retain the hearing aid on the auricle, modify the signal the hearing aid produces and be comfortable to wear. The same article notes that failing at one of those tasks can make the whole fitting fail. AudiologyOnline’s “Earmolds Primer” lists the same objectives (seal, retention, acoustics, comfort, appearance) as the reasons custom earmolds are used instead of universal ear domes.
Earmolds are used with behind-the-ear (BTE) hearing aids, receiver-in-canal (RIC) and slim-tube styles. Because the people ordering them are often clinic or lab staff rather than the wearer, the practical question is usually which of the variables below an order has to name. For the wider list of consumables a clinic stocks, see the audiology clinic supply checklist; for how regulators define the product class, see what is a medical device.
Earmold styles: occluding and non-occluding
AudiologyOnline’s primer sorts styles by whether they occlude (block) the canal. The occluding group, used with BTE, RIC and slim-tube instruments, is canal (“the least visible style”), shell, canal lock, skeleton, semi-skeleton, canal shell and hollowed canal. The primer states that the hollowed canal style is “available in soft materials only”. The non-occluding group is CROS A (“hard materials only”), CROS B, CROS C, advanced design free field (SAV) and the open-fit IROS style.
How the concha and canal portions are described
| Style | Description in the source |
|---|---|
| Standard | Fills the concha (the bowl of the outer ear) |
| Shell | Standard shape with the concha bowl shelled out, mainly for appearance |
| Skeleton | Concha reduced to a ring or half ring that rests on the lateral concha wall |
| Half-shell | Occupies the cavum concha (the lower part of the bowl) |
| Canal | Reduced to the canal aperture and canal portion |
| Canal lock | Canal style with a small tail that rests against the antitragus for retention |
Source: Hearing Review, “Earmolds and Hearing Aid Shells: A Tutorial, Part 4”. The same tutorial adds that an extended helix can be added for retention, and that a ring reduced for appearance can lose retention, break the seal and cause feedback.
Earmold materials compared
Earmold materials, or the material of an earmold, are the second axis. The two audiology sources give overlapping but not identical figures, so the table keeps each source’s wording and marks where they differ.
| Material | Hardness and shrinkage as reported | Tubing and other notes |
|---|---|---|
| Hard acrylic (Lucite) | Hard; shrinks 2 to 4 percent during polymerization and needs buffing (Hearing Review) | Tubing can be cemented (AudiologyOnline) |
| Hard UV light-cured resin | Hard (Hearing Review) | Light-cured (UV) resin is listed as a hard material (Hearing Review) |
| Soft acrylic and soft light-cured resin | About 40 to 50 Shore A (Hearing Review) | None added |
| Vinyl | About 30 to 50 Shore A (Hearing Review); soft vinyl described as “notorious to shrinkage” (AudiologyOnline) | Tubing can be cemented; hard vinyl is reported to soften with body heat (AudiologyOnline) |
| Silicone | Medical-grade silicone about 20 to 70 Shore A and shrinkage about 0.2 percent (Hearing Review); platinum-cure silicone 25 to 60 Shore A, does not shrink (AudiologyOnline) | Needs a tubing anchor or tube lock rather than cement; silicone softer than 25 Shore A “may not be firm enough for insertion into the ear” (Hearing Review) |
| Polyethylene | Hard (AudiologyOnline) | Called “the most hypoallergenic material in the industry” by AudiologyOnline; only available in opaque beige |
| Combination | Hard concha with soft canal (AudiologyOnline) | None added |
Where the two sources give different Shore A ranges for silicone (20 to 70 against 25 to 60), both are shown rather than reconciled.
Earmold parts and what each one changes
Earmold parts are named in “Anatomy of an Earmold” and the Hearing Review tutorial. Mapping each part to what the sources say it affects is the quickest way to read an order form.
| Part | What it is | What the sources say it affects |
|---|---|---|
| Canal portion | The section that sits in the ear canal | The acoustic seal occurs in the ear canal; the tutorial reports that the concha body does not determine the seal |
| Concha and helix | Outer-ear portions of the mold | Retention and appearance; not part of the acoustic seal |
| Canal lock (tail) | Extension resting against the antitragus | Retention |
| Sound bore | The channel carrying sound; sizes named include open, large (3 to 5 mm), standard 2.3 mm and small (about 1 mm) | Acoustic output; a horned bore is reported to improve high-frequency output |
| Fishmouth | Beveled cut at the end of the sound bore | Described as a cerumen trap, not a true acoustic modification |
| Vent | Channel through the mold (parallel, angle or branch, trench) | Low-frequency gain and occlusion; a trench vent is a groove along the canal for drainage |
| Tubing and tube holder | Connects the mold to the earhook | Attachment method depends on material: cemented or anchored |
Variables an earmold order names
Read together, the sources treat these as separate variables, so a specification that leaves one out is incomplete. This is a reading aid, not a recommendation of which option suits any person.
- Style: one of the occluding or non-occluding types above, including any restriction (CROS A hard materials only; hollowed canal soft materials only).
- Material: with the hardness grade where the laboratory lists one, since ranges overlap across suppliers.
- Tubing method: cemented for vinyl, acrylic and polyethylene; anchor or tube lock for silicone.
- Sound bore and vent type: named parts, each with its own acoustic effect.
- Material notes: the sources describe some materials as hypoallergenic, so the order form should carry whatever material information the clinic records.
Common misunderstandings
- A bigger mold seals better. The tutorial says the common belief that more concha fill gives a better seal is contradicted by two studies it cites; the seal is in the canal. The tutorial adds that standard and shell molds, which retain more securely and carry a lower feedback risk, are often credited with a “superior seal”.
- Softer is automatically better. Hearing Review notes very soft silicone may not be firm enough to insert, and AudiologyOnline says soft vinyl is prone to shrinkage.
- All silicone is the same. The sources give different Shore A ranges and name platinum-cure and heat-cure silicone as different products.
- Earmolds and universal domes are interchangeable. AudiologyOnline presents custom earmolds as better on seal, retention, acoustics, comfort and appearance; hearing protection products such as those in hearing protection types are a separate product class.
Frequently asked questions
What are the main earmold types?
Styles are grouped as occluding (canal, shell, canal lock, skeleton, semi-skeleton, canal shell, hollowed canal) and non-occluding (CROS A, B and C, SAV and open-fit IROS), according to AudiologyOnline.
What are earmolds made of?
Hard and soft acrylic, light-cured resin, vinyl, silicone and polyethylene, as compared in the materials table above.
What are the parts of an earmold?
The canal portion, concha, helix, canal lock, sound bore, vent and tubing holder; the parts table above shows what each one affects.
Is the seal made by the concha or the canal?
Hearing Review reports that the seal occurs in the ear canal and that the bulk of the mold at the concha is irrelevant to it, under the conditions the article sets out.
Sources
- Hearing Review, “Earmolds and Hearing Aid Shells: A Tutorial, Part 4: BTE Styles, Materials, and Acoustic Modifications” (Chester Pirzanski; first published 2006, last modified 2022-02-01), hearingreview.com. Checked 2026-10-30.
- AudiologyOnline, O. Uslu, “Earmolds Primer: Custom Earmolds Essentials”, 2018-11-26, article 24101, audiologyonline.com. Checked 2026-10-30.
- Hearing Review, “Anatomy of an Earmold”, 2008-09-15, hearingreview.com. Checked 2026-10-30.
These are professional audiology publications, not standards. Figures are attributed to the source that gives them. For audiology as a field, see speech-language pathology and audiology.
