Pretty much what you'd expect and a good buy for the price - no frills, just a good solid cable. The jack plugs are slightly oversize and have flex strain relief bushings molded directly onto the twin-3mm cable.
Overall this isn't the kind of lightweight extension that you'd just wind up round your fingers and stuff in a pocket, but if you're looking for a headphone extension to keep in the laptop bag or similar it'll take some serious knocks and tugs and last for a long time.