Micron Filter Bags are constructed of a white felt material that has a nominal micron rating for removing physical solids from water. The lower the micron rating of the bag, the more particles it will trap, but the filter bag will clog quicker. 100 micron is great for fish systems and a 50 micron is great for reef systems with minimal fish. All plastic ring bags feature a 1" wide nylon strap across the bag opening that allows for easy hanging of the filter bag.