I use 36gram ones (ridenow from aliexpress) and they're surprisingly great and very cheap. I now carry four replacements when randonneuring and it's still only the weight of one butyl tube. Also, they've become better in the last year between two times I've ordered them - the valve used to be plastic, now it's metal; and they added two rubber washers to fill in the space below the valve, which is nice since that's where they used to stretch and balloon in the space. I use them with a road bike, 700c*25 They do lose air a bit faster than butyl, I'd say about 1 bar a week, regardless if ridden or standing.

edit: haven't tried lighter ones than 36gr. since a friend who did reported they tend to stretch too thin in places when re-pumping 4-5 times.