After leaving the two new tubes inflated all this time outside a tire they hold air fine, they only leak when put in a tire. The one I put in a spare rim and tire leaks down in a day or two.
I inflated it as much as I dare to and stuck the tube in a wash tub full of water and even after 15 minutes I don't see any air bubbles, with the valve cap off. I stretched, twisted and bent the inflated tube all different ways as well under water and got no bubbles. Yet it leaks air in the tire. I've tried it in a tire three times now and it looses air. In comparison, I dug out an old tube, one with five or more patches, that needed another patch to hold air, and it holds air fine. That tube is marked General Tire and Rubber made in Jeanette, PA, it came out of a junk bike I trash picked, an old Scwhinn woman's model that was rusted so bad the tube was showing through the rim. Yet the junk Chinese tube isn't even as good as a dirty, patched, scuffed up tube that's likely 50 years old or more.
One thing I can't help notice is the difference in both weight and size of the old American made tubes and the Chinese tubes. The old tubes are large in diameter buy almost double before inflating, and the rubber is thicker by at least double on the old tube.
The old tube feels different in hand, its less slick or shiny, and far stretchier than the new tube. The new Sunlite tube is smooth, sort of slick and shiny and very hard to stretch compared to the old tube. The new tube also likely has to stretch three times its original size to fill the inside of the tire, where as the original tubes barely have to 'stretch' at all. Some in fact are hard to actually 'stuff' inside the tire as you mount the second bead. The new tubes also need to be stretched around the rim.
They seem to be more a one size fits all deal now.
I suppose the only way these new tubes will be air tight is if I ad some sort of self sealing fluid to them.