What"s in the package? The package includes 1 (one) unit EelVision Polarizer internal flexible foil polarization filter compatible with the GoPro© HERO4 and HERO3/3+ housing only. Accessory will not fit on HERO1 & 2 housings How does a polarizing filter work? A linear polarizer selectively allows polarized light to pass on a certain plane. That"s what makes it different from a regular neutral density filter or a plain tinted film, as those will block all directions. Experiment holding this filter in front of a TV or LCD screen and rotating it! Polarized filters block most of the undesirable reflected light to reduce glare, thus producing true color saturation and dramatic effects. How to install an eV Polarizer? EelVision filters are easy to install and remove! There is no need to unscrew the lens and voiding the warranty. The polarization axis is easily indicated by the tab so you won"t need to figure that out every time you have to (re)install them. The tab helps holding the filter in place and keep it from rotating out of the polarization axis while in use. Not recommended for diving or low light conditions. Disclaimer - This is not a snap-on external filter; - Read and follow instructions prior to use; - Keep filter and plastic packaging away from small children; - Designed for use with GOPRO® products. GOPRO® is a registered trademarks of Woodman Labs, Inc. in the United States and other countries. - Price does not include camera, housing or any other accessories depicted in the pictures in this listing, other than the filter itself.