Rain Flow Total Gutter Protection is a system that fills the entire gutter opening so that nothing but water can get in. When Rain Flow is installed, rainwater passes easily through the material and quickly flows to the downspouts. Leaves, spinners, pine needles, twigs and other debris stay on top but don’t impede the flow of water. Because air flows both under and over the debris, it dries quickly and blows away on the next breezy day. .