I have the version which measures 42/43cm x 47/47.5cm. It is around 28mm thick. The cover is nylon and has a more breathable smooth finish on one side and on the other side is less breathable and has some rubber like beads attached to it to help it grip your chair and stay put.The cover is zipped and removable and could be washed. It has a carrying handle which can be tucked underneath if desired.The cushioning is a honeycomb of soft silicone like material.The overall effect is that this cushion adds padding and comfort and also improves aeration so may be cooler in the summer and reduce sweating.It is not as squishy and comfortable as as say a memory foam cushion would be but the fact that it achieves better aeration does make a signicant difference to comfort and is less hot than a memory foam cushion.This cushion is essentially waterproof and has a wide range of possible uses, inside and out. I am using it on my office chair which whilst padded, is otherwise a touch firm.

Ordered via vine.This is a reasonably thick and typical chair sized "Gel" cushion, entirely washable as the outer material is zipped and can be removed to wash.What's on the inside that actually provides the cusioning is what looks like a square black section something that looka very much like black silicone but it has rows of extended vertical patterned and raised sections all inter-connected - This section can be taken out for washing although the silicone like cushining itself is entirely water-proof.In fact it's exactly like the hexagonal rows within the llisting diagram so I guess that counts as a "Gel" cusion though there isn't any gel of any kind in there, but I can still see this providing some level of comfort as its relatively thick.Though if you already own an expensive gaming chair or similar it might not make any difference or even reduce the ergonomic base if you put this on top of it. So I think this has some limitations, I have no expertise in these type of products but I can see it providing comfort for cheaper work chairs, or even solid plastic chairs like school chairs, though it's unlikely anyone will be sitting any a hard/plastic chair of any kind for a long period of time.It also comes with a handke making it perfectly portable, I'd agree it;s breathable too and the outer cover material is alsio of decent quality. So it's of reasonable thickness that being maleable silicone will collapse somewhat under your weight, and I can see this being useful for many, though not necessarily essential if your chair type is already ergonomically designed.But also for travelling and even on a decent Gaming chair, the size I got is about the perfect size, it would add almost like a memory foam cushioning effect, except not truly memory as the rebound would be instant. I bought this for my parents not myself though I've tested it.But it does seem to do the job that the demo images indicate simply by being soft cushioning, whether or not a thicker or denser layers would have been more effective I don't know, no doubt you can buy thicker versions and many variations of these.And yes I can also see it as being good for a yoga or meditation mat if you are otherwise on the floor, especially the larger 45 by 45 one, for specific chairs you'd want to measure this up but I don't think it;s going to be too wide for many chairs any even then any excess on the edges would be minor and possible contribute further to the cushioning.At £12.99 I think its performance and functionality is justified, but of course at this price it is an entry-level version and no doubt the sky is the limit and more expensive and superiior shapes, designs and versions existing.I'm always a bit skeptable of "breathable" stuff making much difference, but then the hexagonal inner section are hollow so it does leave gaps for air underneath.So I think for what you can do with this, it's easily removable zipped cover and washable, the inner silicone like section cant really be damaged. It's an entry-level cushion in terms of it's low value but I think it's high quality and convient enough with effective cushioning to justify the price. I expect thicker verions like this with double the thickness exist, but they you are sacrificing on the weight/portability somewhat unless you intend to use this permanently and fixed on a chair, which I can see providing some benefit for sure.So again, this happens to be the first chair/surace cushion I've reviewed, it's an inexpensice one but if you work all day on a very cheap basic PC chair like doing admin, then with this ontop/underneath it's going to be much more comfortable as it does what it demonstrates in the images when the pressure of your weight is on it.I think it;s worth paying £12.99 for, or ore for the larger one, if I had to sit on a cheap work provided chair each day then I can see this being really useful, and for travelling and as a yoga mat and pretty much most PC/desk chairs exceot maybe very high end and ergonomic ones that have something simlar to this or memory foam already integrated, which is quite uncommon.So it can be a rather cheaper way to improve comfort, potentialy even reduce pain, it arrives folded up so you can either carry it with the included handle or it would quiote easily be folded to fit into many bags.