I also have tires that are 29x2.0 and 29x2.1 ... I wonder if the tube is fit for those sizes ?
Thing is that I cant find any specific lightweight 29" tubes but I have seen some very lightweight 700 and 26" tubes that might work.
I already have 700x47 that weigh 95 gr.
I have also seen some lightweight 26" latex tube that migth work.
You could use those tubes on wider tires, probably up to a 2.5 but I wouldn't recommend it- nor would I use a 26 inch tube unless you enjoy getting more flats.
Ideally a tube inflated just enough to give it shape will completely fill the tire. A skinny tube has to be overinflated quite a bit before it will even contact the inside of the tire. Think of a balloon inflated real tight. Touch it with a pin and it will explode. The same balloon barely inflated has to be pushed much harder with the pin to pop it.