A lens filter for your action camera has various functions. Some lens filters protect the glass of the lens of your action camera. That's useful if you use the camera during rough sports, such as mountain climbing. There are also lens filters to add an effect to your video footage. You can increase the image angle of your camera with a wide-angle lens, for example. An ND filter reduces the amount of light that enters the lens. That way, you don't get overexposed images as fast when you're skiing. Carefully consider what your usage situation is and which filter suits you.