Contrary to popular belief, Yonex pre-strung badminton racquets are NOT pre-strung with Yonex BG65.
Virtually all of Yonex’ pre-strung badminton racquets are pre-strung with something called Yonex Demo Gut — a low-cost, extruded nylon monofilament that is nothing at all like Yonex BG65 multifilament.
Yonex Demo Gut is not intended for long-term adult use. It is a temporary string put in racquets to help them keep their shape and to help large sporting good stores sell racquets.
Yonex Demo Gut is not intended to function as badminton string in any serious way.
You will not find serious players at the professional or recreational level stringing their racquets with Yonex Demo Gut.
In fact, Yonex does not even sell Yonex Demo Gut.
The name tells you all you need to know. Demo Gut was created as a demo string. Essentially, it is a prop. It is a substitute for the real thing.
So when you buy a pre-strung Yonex racquet, you should plan to replace the strings in very short order.
What you replace it with is up to you. It will depend on the racquet you are stringing, the shuttles you are using, and what you need the string to do.
Yonex has an large selection of excellent badminton strings to choose from. Regardless of who you are or how you play, we will be able to help you choose a suitable replacement when you are ready.