The standard KTM Duke 125 exhaust sounds pretty good but a popular add-on is replacement performance silencer. Whether you want a full system or just a slip on end can you can start your search here with loads of replacement exhausts and silencers made from carbon fibre, titanium and stainless steel.
Manufacturers of replacement KTM exhausts include Akrapovic, MIVV, Arrow, Scorpion, Toro and many more. Before you buy a new pipe for your bike please make sure that it complies with the regulations and laws in your country.