(Size: (W) Top 11.4"/Bottom 11.8" X (H) 19.6 " X (D) 6.3" cm " = (W) Top 29 cm/Bottom 30 X (H) 50 cm X (D) 16 cm)
On my test home in the pouring rain it's very water resistant but the seams aren't sealed, so some water gets through. Soaked it in Nikwax TX Direct today, and will look into seam sealant, or just use a rain cover/dry bag inside.
Local tk maxx has Puma Traction roll top backpack in camo with blue front for £16.
EDIT:
Bought one for the capacity.
It's this one: https://www.amazon.co.uk/Puma-Traction-Backpack/dp/B00ATBKNZW
Label says "Cordura Brand Fabric", and has rubber coating on the inside.
On my test home in the pouring rain it's very water resistant but the seams aren't sealed, so some water gets through. Soaked it in Nikwax TX Direct today, and will look into seam sealant, or just use a rain cover/dry bag inside.