“After dyeing, the fabric is finally treated with a durable water repellency finish (DWR) on both sides of the fabric for added performance and water resistance.”

“Restoring Water Repellency
Through hard wear and tear, Ventile garments may eventually require a reproof. We advise that you follow the specific instructions on the waterproofing products we’ve suggested below:

Granger Extreme Waterproofing for Naturals
Nikwax Tech Wash or pure soap (ensure there is no residue of detergent in your washing machine)
Nikwax Cotton Proof”
From
https://ventile.co.uk/fabric/
If I understand correctly, this pertains to the UK originated, currently Swiss/Austrian ( Stotz & Co. AG)made Ventile version. Various treatments are applied to Ventile it depends on the manufacturer. The Japanese versions of ventile may be different but it’s harder to research.

“After dyeing, the fabric is finally treated with a durable water repellency finish (DWR) on both sides of the fabric for added performance and water resistance.”

“Restoring Water Repellency
Through hard wear and tear, Ventile garments may eventually require a reproof. We advise that you follow the specific instructions on the waterproofing products we’ve suggested below:

Granger Extreme Waterproofing for Naturals
Nikwax Tech Wash or pure soap (ensure there is no residue of detergent in your washing machine)
Nikwax Cotton Proof”
From
https://ventile.co.uk/fabric/
If I understand correctly, this pertains to the UK originated, currently Swiss/Austrian ( Stotz & Co. AG)made Ventile version. Various treatments are applied to Ventile it depends on the manufacturer. The Japanese versions of ventile may be different but it’s harder to research.