The standard inner is lightly coated breathable nylon ripstop at about 32 grams per square metre. I do not think it is really breathable enough and would add some closeable mesh panels for adjustable ventilation.
Expense aside if I used say 17 gram /sq m cuben (0.45 ounce/sq yd I think) I could save about 75 grams (3 oz) If I increased the mesh vents a little and ensured that only say 80% of them were closeable would there be a problem? What do people think?
Which cuben is equally strong to the 32 gram ripstop? I was imagining a vent each end and the top of the door total mesh 0.75 sq m. Maybe partly closeable with 13 gram cuben?

It may work, but I think if you're going to go this far you might as well go all the way to a single-wall tent - you have nearly the same ventilation issues and you cna get it lighter. On the other hand, you can think of it the way Bill Stephenson di when designing the Warmilte tents. they are double-wall with both walls non-breathable - the idea being that having two layers keeps the inner layer warmer and thus less likely to have condensation form on it.

Yeah, maybe.
(17 gsm is 0.50 oz/sq yd according to my sums.)

Need to be able to SEAL the windward end against spindrift, but this applies equally to breathable nylon.

Certainly would need to pay more attention to ventilation in the field - but to be honest I can't see that as a problem.

Mind you, the 70 g you save is not a real lot for all that expense and hassle. Real problem is, as someone said recently, the inner tent is not that big a fraction of the whole bundle.

Cheers

Thanks Roger and Paul,
all that is about what I think. I am in the midst of making a cuben Breen 25 gram/sq.m single skin 2 person Mid tarptent with a side enclosed porch without midge protection. When I have tried that I will either have to add midge protection to make a single skin tent or as a separate inner. The difference in weight between the 2 options is the weight of the inner walls, less midge proof inner door.If the inner wall is cuben it may only weigh 60 grams more, if it is standard nylon nearly double that. The separate inner leaves the option of leaving the midge protection behind and as Paul says should reduce condensation and be warmer. I am hoping that the outer with guys will be 230 grams the groundsheet and midge netting maybe 170 grams. The cuben inner walls would add about 20% the nylon ones add 40%. In damp cold Britain on still nights we get condensation on the inside of our Laser nylon inner with all vents open. I am not sure the maybe slight breathability of the standard version is worth the extra weight.

Edited by Derekoak on 01/24/2010 05:29:20 MST.