Plush toy also called soft toy, and filling machines also called teddy bear stuffing machine.
For fiber material for filling: polyester staple fiber
There is 7D, 6D, 15D, also have grade A, B, C.
Usually plush toy maker prefer 7D, A grade.
If want very strong plush toy, you can adopt 15D polyester fiber.
Because 15D polyester fiber is thicker, harder and stronger.
Low-end plush toys filled with B or C grade PSF fiber.
As per the length of fiber, there is 64mm and 32mm polyester fiber for soft toy filling.
64mm good to filling by hand, 32mm is good to stuffing by machine.
So if you prefer the plush toy stuffing machine, 7D 32mm polyester fiber is a good choice for you.