> e-mail the kite building site and they said all of their ripstop was coated
Yes, a LOT of very light synthetic fabrics have an acrylic coating **just to keep the weave together**.
Caution: acrylic is NOT a waterproof coating, just a 'stick it all together' coating. However, it does tend to reduce any airflow to nearly zero. Good for parachutes maybe and for kites; not good for most outdoors gear.
> momentum would not be a good choice for an inner tent
Why? Yes, Momentum is calendared on one surface, and that will reduce the air flow somewhat. But it IS used for sleeping bags where some air movement is crucial to letting the water vapour out. Also it has a a good DWR on it. So I cannot see why it would not make quite a good inner tent fabric. It may be a little more expensive, but in the quantities used by an MYOG enthusiast the differential is trivial.
> 1443 tyvek as an inner tent
Welll, one thing is for sure: it will NOT breathe nearly as well as Momentum! A non-breathing inner tent ... with me inside it?
> 1.1 osy ripstop nylon is the most frequently used.
Well, yes. I use 32 gsm (0.92 oz) fabric from Carrington Mills (UK) for my inner tents: it has worked excellently. If I had Momentum fabric I would be happy to use it.
But I would NOT use Tyvek: it does not pass air. Could be deadly!