I use a Supracore "Stimulite" Contour cushion, 18' x 18" I've also used (actually still do, I have several of these and rotate them as I need to wash them) the Contour XS version.
Both are silicone(?) rubber 'honeycomb' cushions, and the same basic 'butt' shape. The claimed theory is that the cells in the honeycomb collapse under the areas that are loaded more heavily and less so under the light areas, so that you end up with uniform loading over the entire sitting surface. It isn't perfect, but seems to work pretty well when I've done pressure mapping... I got a slightly better mapping w/ a ROHO, but not by much, and I have the same sort of concerns as BM about the (lack of) stability, transfer problems and vulnerability to shop debris...
The cushions have multiple layers of honeycombs that vary in how hard they are, with the thickness of the different layers changing in different parts of the cushion.
The big difference between the regular and XS versions is the XS version has a layer of softer honeycomb on top, I find that I seem to fully compress that as soon as I get on the cushion so the regular version seems to give me a little bit more support.
I seem to sweat a lot, and with any of the cushions I've tried that have 'incontinence' covers my butt ends up soaked... The standard Supracore cover is a breathable fabric (feels like polyester or similar synthetic) and the honeycomb is breathable. Supracore claims that the honeycomb is actually designed to have a 'pumping' effect when the user moves around in the chair, or is moved by the chair movement when going over bumps, etc. that increases the air flow.... Either way my butt stays a lot drier when sitting on these cushions. Downside is that if one has an "accident' (neurogenic bowels are SO annoying that way!
) the cushion gets soaked... However the cushion and cover are all machine washable, and machine dryable (the machines have to be large and non-agitator style to handle the cushion) but I find that it works if I just hose it down w/ plenty of soap and water in the shower. It then takes a couple days to air dry, so having enough to 'rotate' helps. They also seem to lose some of their support after a year or two (or at least that is what the insurance will cover....)
I've never had a cushion related pressure sore... I had a small sore on my coccyx in rehab from the shower chair (solved by rotating the cushion to a rear opening) and a weird thing from "necrotic fat" on a non-sitting area of my butt shortly after I got out of rehab.
I have tried several cushions in the first few years after I was hurt and none really worked well....
When I tried a single chamber ROHO I also found that other than boosting completely off the seat I couldn't really do any sort of pressure relief as the air just moved around as I shifted so the pressure points stayed the same. I didn't try a fancier pump, but the stock "jumbo syringe" style pump needed so much effort to operate that I could not inflate the cushion while on it. (I found this out when a slow leak in the valve left me bottomed out) I consider this dangerous, especially if you don't have enough feeling to be able to tell that you have bottomed.)
I tried one of the 'hybrid' foam / air cushions (I forget the exact brand, it is still sitting in the back of my closet somewhere) and it was OK but not great, especially as it was hard to get the air pressure right. It did have a MUCH better pump setup. It used a squeeze bulb like a blood pressure cuff, and that didn't move a lot of air per squeeze, but the effort was low and it was easy to pump it up while sitting on it... The bulb was also compact enough to fit nicely in the front pouch of the cushion.
I also tried a couple of different foam / gel cushions like the Jay type, and found they mostly weren't comfortable, primarily because they didn't allow any air circulation to dry my sweaty bottom...
ex-Gooserider