I had made some assumptions about waterproof materials, that turned out to be mistaken. At Mt. Rogers my DIY overmitts leaked and the possum down gloves inside them got wet, so this week I set out to seal the seams between the yellow silnylon and black "white widow" pack cloth I used for the palms. I applied Permatex Clear RTV Silicone Adhesive 66B to all seams, then dunked my hands in water to test. They leaked. I had also sealed the seams of my old DIY Tyvek mitts, so I dunked them, too. They also leaked. I hung them up to dry overnight, then filled them with water today to locate the spots I had missed. Surprise - the black fabric leaked everywhere. Despite having what looks like a urethane coating on one side, it's not waterproof. I also tested the Tyvek mitts - same story. The material (admittedly much worn and wrinkled) leaks. The coated seams may be the only parts except the yellow silnylon that didn't leak.
Attached photo shows them drying on the line. (By the way, that's my hammock workshop slowly taking form in the background. I'm assuming the new roof doesn't leak.)
I had sought to make the mitts less slippery by putting stripes of silicone across the palms. Those parts didn't leak either, so now I need to go back and fill in the spaces between the lines. My pulk bag is made of the same white widow fabric, so now I know to use drybags for the stuff I put inside it. Live and learn. Life is full of problems and partial solutions.