I haven’t ventured to the bikini or underarms yet. The part that holds the earcups is made of a thick plastic material that is attached to the actual war cup. But if you’re wondering if they might be too narrow and on the fence about buying them, they are goNna be too narrow. Turned my redundant AirPods into an everyday use. Ive removed the inserts and replaced them with my orthotics. However, I would not recommend this style as the top strap was very uncomfortable and gave me blisters on top of feet on the very first wear. Tried these on playing on a PS4 and on multiple games and I am very impressed! It those want it needs to do, surprise it looks just like the original still holding up The earpieces feel re-assuringly solid but well machined. It only takes a big splash in a puddle to ensure that socks get soaking wet!