Open fit hearing aids have very thin tubes that enter the ear canal and smaller cases that rest behind the ear, making them barely visible. Additionally, hearing aids that sit within the ear canal can now have greater ventilation.
Open fit hearing aids are similar to BTE devices. They are small when compared to normal hearing aids. In open hearing aids no ear mold is involved and it is connected to a small tip that holds the tube inside the canal. Mostly tip is made of very soft materials like silicon. If you want to know more about open hearing aids check this link http://www.hearingsolutions.ca/products/hearing-aids.