The no sag cushion is a real 'wonder-find'. I now have two of these, one for the back and one for the base of my wheelchair. Even though my wheelchair is relatively new, it is in constant use and both the back and base slings already have considerable 'sag'. I had no idea that the Essential Aids no-sag cushion would make such a big, big difference - it's marvellous. I think that the Essential Aids no-sag cushion is a necessary requirement as a base to whichever seat cushion is chosen, enhancing the life and performance of the seat cushion. I would like to award five stars for swift service, realistic pricing and, most especially and importantly, items which are 'fit-for-purpose'.