In reply to mickeyluv:
> I thought you weren't supposed to proof ventile as the fabric absorbing water and swelling is what seals it?
That's an arguable point.
As for the historical development of Ventile, well, originally, there were two forms; bleached and unbleached. The bleaching process removes the natural cotton oil from the cloth, and, as a result, it wets out almost immediately. This bleached version was used to make lifejackets stuffed with kapok, and the reason the wetting was wanted was to form a barrier to oil penetration, which otherwise saturated the kapok, rendering the lifejacket useless for sailors fleeing ships sunk by shelling or torpedoes.
The unbleached version was used to make immersion suits, using the natural water repellence to stop the suit wetting out. One might argue that an immersion suit might also have to deal with oil, but pilots tried to parachute to safety, and, if their plane landed on the sea without them being killed, the chances were that it hadn't broken up, so the oil spillage would be minimal.
That's the story told by Don Robertson, formerly of the Defence Clothing & Textiles Agency, in his DofE book 'Workshop'. Since his job was researching fabrics and developing clothing for the UK military, I'm hoping he knows what he's talking about. And his view is that Ventile doesn't work as a waterproof by wetting out and swelling, but by being a natural microporous fabric, due to the very close weave using long-staple cotton threads. He also says that a Ventile suit that has genuinely wetted out, causing the fibres to swell is very stiff, and impractical as a garment.
And this need for water-repellent treatment for Ventile waterproofs is backed up by Toerag's quote from the manufacturers.
