The Standard Day ND/CPL 4-Filter Set for Sony RX0 II / RX0 from Freewell includes an ND4, ND8, ND16, and CPL filter for capturing more accurate images outdoors. The ND (neutral density) filters function as shades that darken the image a bit to compensate for sunny conditions. They cut the amount of light hitting the camera sensor by 2, 3, and 4 f-stops, respectively, for varying degrees of sunlight intensity. Without the reduction, your only option would be to use much smaller aperture settings and much shorter shutter speeds (or your image will be washed out), but this isn't preferable because these settings would need to be on the extreme end and the results might have issues with them. But with the appropriate ND filter used, you can assign normal aperture and shutter speed settings and capture accurate images. Moreover, the right ND filter can allow you to set unusually large apertures and long shutter speeds for long-exposure photography.
The CPL (circular polarizer) filter helps prevent unwanted reflections from naturally reflective outdoor surfaces, such as windows, bodies of water, and snow. One of the benefits of this is that you can shoot through windows, such as through a car window to capture an image of the driver. Normally, the sun reflecting off the window creates a glare that prevents getting a clear image in such instances. But a CPL filter removes the glare and allows you to shoot through the window. Similarly, when, for example, shooting a streaming river, with a CPL filter you can actually capture the large rocks under the surface of the river. CPL filters also help reduce haze and capture increased color saturation, such as when shooting the sky, so that the blue of the sky is seen more accurately. The CPL filter rotates to adjust for varying amounts of glare to let you compensate for different sunlight conditions. The filter is marked with polarization indicators on the frame for this.
All four filters are made with premium optical glass and are multi-coated with 16 layers of coating for waterproof, dustproof, scratchproof, and oilproof quality. They feature an aluminum frame and have an efficient snap-on system for easily attaching and removing them.