A thick plastic cover, clear, with heavy duty grommets and bungie cords to keep it in place. As is typical with Omlet, there are design details that only make sense when you install it. In this case, the free edge of the cover inserts right between the mesh of the run and the ridgeline of the coop, so there are no drips between the coop and the cover. Only regret: wish I'd ordered two to cover the length of the run. This 6' cover doesn't go all the way to the ground, so some snow does drift into the run along the edge.
I have a dark cover on my run but wanted to let more light in when I added an extension. This is perfect. It's been up for a month in strong sun and high winds and still looks like new.