Remove the patio cushions from outdoor sofas and lounge chairs. Find a clear, dry spot to work, or take the cushions inside to a craft table. Take upholstery fabric scissors and carefully cut one end of each cushion open---if there is not a zipper on the cushion allowing easy access to the foam inside.
Remove the cushion. Inspect the cushion for water damage. Look for darkened spots, which would indicate mold. Soak a mold-covered cushion in a mixture of bleach and cold water to remove the mold. Take a cap from an empty bottle of laundry detergent and fill it with bleach. Mix two cap-fulls into a utility tub or large bucket half-full with water. Make sure the cushion lays flat and is completely submerged.
Use new upholstery fabric---something that can easily be sewn, but is durable enough for use outside. Make sure to choose several yards of fabric in the pattern of your choice; 4 to 6 yards of fabric is generally enough to cover most outdoor patio furniture sets.
Take the fabric and measure the cushions. Cut enough material to cover both sides and edges. Sew pieces together on a sewing machine.
Reinforce the edge along the seam to strengthen. Leave one end open to insert the foam or cushion. Insert the foam, and sew shut the open end by hand. Repeat for other cushions.
Replacing Chair Fabric
Tip an upholstered chair without cushions onto its side. Remove any nails holding the hard seat of the chair in place a claw hammer, unless the seat pops out easily. Remove the seat
Remove the stapling holding the fabric to the seat with needle nose pliers.
Apply new upholstery by stapling the new fabric to the edges of the seat with a staple gun, pulling the fabric tight as you go. Trim off excess fabric, and staple the remainder of fabric in place along the base of the chair.
Replace the nails holding the seat to the chair.