Pennine Outdoor in the UK has a "P2B Feathereight Breathable Nylon" weighing 70 to 90 grams per square meter. It is listed under "waterproof" fabrics. Sent them an eMail inquiry, but got no answer.
The Momentums have a DWR coating, but isn't calling them "waterproof," a bit of a reach? If you want to call them waterproof, you might also want to look at a 1.36 oz. polyester that Fabrics'n'stuff in the UK sells that has as hydrophobic a DWR coating as any I've seen. Water will not sit still on it. But, using any of these DWR treated fabrics as the only protection between us and the elements = bad idea IMO.