Cut a pattern approximately 42 inches long and 15 inches wide. I joined the part that was to be the seat with the 300D to cut down on weight. Taper from the seat portion to top down to about 11 inches across. I created a cup to hold the trekking poles out of the 420D Robic and sewed that before hemming the edges for a finished look. I sewed a piece of velcro for rolling it up when stored. It is extremely comfortable, well worth the 3.4 ounces it weighs.