Ah yes, Ventile. Memories of the 1960's come flooding back. D flashlights. Trapper Nelson Pack Boards. Hyperventilating while blowing up the air mattress each night. Wool.
Ventile is a dense, 100% cotton, uncoated fabric. In theory, as it encounters water, the fibers swell, and block penetration. In fact, once saturated, it will leak wherever it touches anything -- like you -- which breaks the surface tension. This is the same behavior as exhibited by cotton tents. That is why Ventile fails the test for the rating "Waterproof" and barely meets "Water repellant." (Vendors fudge by using undefined terms like "Weatherproof.") Ventile becomes a sponge in prolonged, heavy rain. Used as an outer layer with a breathable, waterproof liner, it becomes VERY heavy when saturated and prevents breathing by the inner liner. Hence, Ventile ceased to be a major player in the outdoor garment market a generation ago. It hangs on in Europe - especially the UK.
As for military usage as an endorsement, remember that the military took 30+ years to adopt padded weight-bearing waist belts on their packs. Actually, it's more like 130 years. An Army surgeon tried to sell the military on transferring pack weight to a heavy cotton waist belt via wooden struts during the U.S. Civil War. Then there's the "deadoption" of magazine rifles as soon as the Civl War was over. Military intelligence should not be used to select kit.
For use where heavy rain is not anticipated, Ventile is quite good as it is wind-resistant and quite breathable -- as is uncoated Nylon which costs a fraction of the usual price for Ventile. Ventile is more resistant to flame than Nylon. Cotton is less resistant to abrasion and less strong than Nylon.