A picture is a thousand words here. Illustrated here are the 3 most common louver blades types that are used in Western Canada. From left to right, they are as follows: 1) Model D4493 Drainable Louver. These louvers are designed to collect water that flows down the individual blades and disperse the rainwater through channels to the mullion and down to the drain. 2) Model R5455 Storm Resistant Drainable Louver. Where superior storm resistance and no water ingress can be toler