J4 cables are reinforced with kevlar to resist breakage. The flat design helps prevent kinks, as the cable coils rather than twisting or bunching. Also, tough and flexible reinforced exoskeletons protect the cable connections and joints.
The SE215's 6.4-ft. cable is very thick, and further reinforced at the left/right split point. Reviews confirm the durability benefits of its heavy-duty design. If it ever does break, the cable is built to detach safely from the earpieces, allowing replacement.
The IE 800 cables are soldered into the earpieces. There is a jack where left and right cables come together, and the remainder of the cable can be replaced, but damage above the split is not user-repairable.
While some sets of earphones are manufactured to break quickly, these are made to last. While there are no outstanding qualities about their build (like kevlar reinforcement), they still meet expectations about how long earphones should last.
There are tons of stories from customers that talk about how they supported their warranty after decades with no receipt, at only the cost of shipping and handling. Koss really means it when they say lifetime warranty.
These originally appeared on Kickstarter as "IRONBuds", for which the company never delivered on their promised product. What they did deliver suffered from poor construction quality, and looks exactly like what is pictured here. The custom components that allow the parts to be swappable