Since I am completely immobile , it is essential that I sit on a cushion that prevents sores. There are various types but by far the best ones are those that vary the pressure. Cushions begin from the very basic to orthopaedic foam, air-filled, gel-filled and variable-pressure. Mine (the one I shall describe) is of the variable-pressure type and although more expensive than a simple foam or gel cushion, it is far better. Here is a short video of EASE CEO (Rex Taylor) talking about his product.
I got my cushion from EASE Seating Systems and it is the G4 model (now discontinued). I chose this model because it can be powered by an external 12V power source that can easily be taken from my wheelchair batteries (I also ordered from them a 24/12V converter). The cushion itself is made of an air bladder made up of many sections that are interconnected : all the even compartments are connected together and likewise all the odd ones. Then there is a power pack that contains a compressor, control circuitry and a battery. The compressor first inflates the even compartments, then after 4 minutes the even compartments are vented off in the odd comartments and finally the odd compartments are inflated by the compressor while the even ones are deflated completely. All this cycle is controlled by the circuitery in the power pack that also houses the compressor.
At first I was a bit worried about the noise of the compressor, but it is only 42db (less than ambient noise) and it runs for 16 seconds every 8 minutes - hardly a niusance. I can say the cushion is excellent...one can forget he/she is sitting down and the compressor is audible only if one is alone in a room. Unfortunately after only nine months` use the cushion began leaking and I had to send it back to the manufacturer for repair under guarantee. The repair was free but I had to send it to America......after getting a few quotes, the idea of courier was dropped because it was far too expensive. In all it took two months to repair it - not because of the manufacturer but because of the slow postal service.