SUNDOME Humidity Dome Multi-Vented - 2in - Black SUNPACK’s Blackout Humidity Dome helps conserve watering while providing an appropriate blackout period. The multiple vents are perfect for adjusting the growing conditions for your seedlings. Humidity domes are a helpful tool to use during germination, often used in conjunction with heat mats. They help protect the seeds, maintain moisture levels, and create the perfect environment for those seeds to get a great start.