The addition of a soft canal to an acrylic mold reduces unwanted feedback due to facial movement while retaining the advantage of the rigid earmold body. Excellent for active children in any fitting, as a hard mold could cause injury if the ear were to be struck while playing. Vinyl will shrink with body contact and age, and can harden and discolor as well. Tubing is often difficult to remove for replacement, and new tubing installation normally requires a highly toxic solvent if cementing is desired. Special locking devices can sometimes be used to eliminate the cement, provided they do not distort the shape of the earmold.
Regular silicone solves most allergy cases, and is comfortably flexible.
A tubing lock required as cement does not adhere to silicone. This is the purest silicone available. For the toughest power aid applications, use soft silicone material in a canal or canal-shell style. Because of its unsurpassed comfort, this material is replacing the Vinyls in many applications, even where high power hearing aids are not being used. Polyethylene is a hard material, appropriate for severe allergy cases.