The Big Agnes Blacktail 4 Footprint is a ground sheet for the Blacktail 4 tent. It's like adding an extra life to your tent floor, protecting against damage, dirt and water. Lay it out, pitch tent over top. So easy and could save a headache down the road. Features of the Big Agnes Blacktail 4 Footprint The footprint also enables you to pitch a lightweight, Fast Fly shelter while leaving the tent body behind