Porous Pave is a recycled rubber, permeable surfacing product. The City of Calgary has replaced over 2 dozen steel tree grates with this breathable, environmentally safe product so far. Porous Pave allows large amounts of water and oxygen into the root systems of the trees, and will bend as needed with root growth and ground heaving, and is an excellent alternative to steel grates that can become dirtied with litter and cause tripping hazards.