Leaks from your dryer vent pipe are a result of condensation, but they can be prevented by dryer vent insulation. The warm, damp exhaust air from your laundry will form droplets of moisture when it touches the cold surface of the vent pipe. Packing the pipe in insulation and improving the seal at the exterior of the building will keep the air warm until it is outside.
Step 1 - Wrap Pipe in Insulation
Track the exhaust pipe from your dryer until it leaves the house. You may have to cut through drywall to fully expose the pipe and be able to apply insulation. Cover the pipe in two to three inches of fiberglass insulation. Secure the insulation with HVAC duct tape.
Step 2 - Seal Exhaust Opening
Your dryer exhaust may be set in a sheet of metal or plywood. In some cases, only a swinging metal “flapper” separates interior from exterior. Improve the heat efficiency of your dryer vent by sealing around it with caulking or foam insulation.
You can also install a vacuum seal that will prevent backdrafts of cold air when the dryer is off. This seal resembles an upside-down cup sitting on a short pipe.