Bests & Worsts Reviews from Amazon

If your roof is mostly long slopes down to the gutter with no valleys, this stuff works great. If you have valleys or downspouts that come down from upper levels with a concentrated flow, it can cause isolated overflow problems. In my case, those were less of a problem than overflow everywhere due to clogs though. What I found from having it in place for two years is that "sheet flow" into the gutters, even during heavy downpours, is drained away exactly as advertised. Leaves and other debris will collect on it, but not to the point of clogging, and will indeed blow off when dry. The problem occurs during really heavy rain where there is a valley or downspout from an upper area that concentrates runoff in one spot. In those situations, debris can cause water to flow over the top. Brushing it off with a broom is all that's required to fix that. There's an additional problem when the point of concentration is too far upstream from the downspout. In my installation, there are two locations where the distance from concentrated flow to downspout is 20 feet or more. When the foam is clean, the concentrated flow will flow into the gutter just fine, but the length of foam it has to flow through to reach the outlet creates too much of a restriction and water backs up. An adventure up the ladder during a heavy rainstorm pointed out that at the high end near the point of concentration, the gutter was completely filled to the brim and pouring over, while 20 feet away, it was less than 1" deep. My solution to open up more flow area, and so far it's working, is to cut the wedge shaped foam into an L shape using a utility knife. See the picture I've added. Don't cut the top part too thin or it will sag.