First and foremost, it is critical that you have treatment with a filler that is specifically designed for the lips. To allow the lips to move and feel natural, a lip filler should be soft and flexible. On the other hand, a lip filler must not be too soft since it must be able to maintain the shape of your lips. To get the correct appearance and feel of the lips, the injector must strike a balance between softness and flexibility on the one hand and hardness on the other hand.