Strong orange rubber to replace the original one. But I didn't use mine yet. Beautiful strap, and with that you can change the orange 24 mm for another brand in your Suunto Core. The aluminum link is the most important part in my opinion....just a litle bit expensive for U$50.00.
But you don't have choice with Suunto. If you like to change the original black rubber strap, you need this strap to use the links