I recently bought a 'tween-season (long) pair of cheap pyjamas. made in Bangladesh. These were made from a knitted single-Jersey cotton (I detest woven pyjamas with a fly). I was surprised to find that the groin area was very generously cut and very soft, almost silky, it is so fine. A full erection is easily accommodated with a little tenting, but my dick is not forced upwards or flattened.
This morning, I woke up with my usual hard woody and I felt the tent and found that just moving the bottom side of it slightly caused the soft cloth to rub gently on the frenulum, a very pleasurable sensation, so pleasurable that I shot my load within about half-a-minute, right into the pyjamas. I have never experienced anything like this before in years of wanking, including with underwear of all types. The down side of this great sensation was peeling off my wet and sticky pants!