Add additional stuffing to the futon by unzipping the cover and inserting additional foam or batting into the mattress. Batting and foam are available at any sewing or craft store. Since the mattress becomes compressed after extended periods of use, adding stuffing not only tightens up the cover by expanding the mattress but also provides additional support for seating.
Stand the futon up on the bottom end, and hold only the cover, thus forcing the mattress to the bottom of the cover. Fold over the excess material, and set the futon mattress back on the futon.
Gather excess cover material on one side of the futon cover slightly towards the back and out of view.
Attach one side of the sheet clip to the gathered material to secure it into place.
Gather any excess cover material on the other side of the mattress slightly towards the back and out of view.
Stretch the sheet clip across the back of the futon mattress, and clip it to the excess fabric.