A lot depends upon the humidity where you live. I'll bet it is really high most of the time in your part of GB. If you lived in the desert (Mojave here) you could soak your shirt until it was dripping and by the time you rode a few miles in the summer it would be completely dry, including the back. I do that frequently. All of my recumbents have mesh seats. I've ridden them in places where the humidity is closer to normal and not had my back get soaking wet but it will get damp. I avoided recumbents with hardshell seats because I read of people riding in a pool of sweat with hard seats.