A heavy duty plastic dome that is 2 in. and fits on 10x20" tray. It will help retain moisture and heat to improve germination of seedlings.  Comes 25 a pack.

Hydrofarm is the nation's oldest and largest manufacturer of hydroponics equipment and grow lights. You can find their products in hundreds of stores and catalogs across North America. Hydrofarm Quality: Their systems incorporate only premium quality components, and the professional-grade hydroponics and UL-listed lighting fixtures will give you years of dependable service. Hydrofarm Reputation: On the market since 1977, Hydrofarm brand products are the choice of more indoor gardeners and gardening retailers than all other brands combined.