There is nothing that presents a concern about them breaking. Sennheiser made sure to use sturdy and high quality plastic.
Judging its build quality by the price I managed to get them at (~€140), the build quality IS something to write home about. It truly is a great overall choice, it's non-fatiguing, very comfortable and enjoyable to listen to. If you catch these at a discounted price, they are a steal. In the sub-200 USD category it's a king of its own, and this is how many people perceived them as for years. The Sennheiser HD 598 is an entry-audiophile headphone from the well-known German manufacturer, Sennheiser.