Slips under your MSR® Hubba Hubba tent to protect the sewn-in floor from wear and tear. Also allows you to set up the tent fly, without the body, as an ultralight shelter.
The standard test for coated fabrics uses a standing pipe (column) filled with water. The figures given are the water column height. A 1000mm coating allowed no leaks after 1 minute under 1000mm of water.