Closed style ear domes do not have any vents. The lack of vents prevents non amplified sounds from entering the ear canal. The closed dome allows for more aggressive amplification, up to 15-10db more, especially in lower frequencies.
Best for those with a more moderate to severe hearing loss due to the increased amplification provided.
Magic style ear domes are a hybrid open / closed ear dome. It looks like 2 domes stacked on each other with small slits rather than large vents as found on open ear domes. Overall, magic domes offer the best of both worlds as compared to open and closed ear domes.