I have recently received a set of patio furniture from my parents. It was in good shape and I have a large yard and love to entertain. They had recently cleaned the seat cushons, but the vinyl straps were looking a little yellow and dirty. The best way to clean the vinyl straps is mix up hydrogen peroxide and water in a 50/50 mixture. Wipe the mixture all over the straps and let sit for about half an hour. Blast your furniture clean with the garden hose and high pressure attachment. If more whitening is required, repeat the hydrogen peroxide/water soak for another half hour.
