I had two reasons for trying Kleinerts.  I purchased a competing breathable product some time ago and was quite disappointed with the workmanship; if worn with the seams on the inside, the tag at the back was exposed, and there were some other problems as well.
The first expedient I had tried was a cheaper vinyl/plastic 3-pack for under $10.  These created so much sweat that they were extremely unpleasant to wear, so when I read that your brand purported to have overcome this problem, I decided that it was worth the price to give them a try.  They arrived yesterday just in time for me to wear them to my doctors appointment, and while I cant as yet testify to their actual effectiveness (surely I don't need to be more specific!), I can state that, as advertised, they do not create heat.  In other words, no sweat!
My only quibble is that the rise could be a little higher; they don't quite come up to my waist in back, but in view of the advantages mentioned I consider this to be an extremely minor issue!
Thank you for the sizing tips, and thank you for providing a product that not only addresses the problem, but takes the comfort of the customer into account as well.  I will be purchasing another couple of pairs within the next few days.