Rubber over a thin black NYLON base for complete waterproofness and permanent shape-keeping, no matter what. The C67 here is the widest Brooks  Cambium/Vegan saddle and for most riders, the best vegan choice for upright riding. 

We can't guarantee your butt-n-crotch comfort but it's wide and flat, really supportive, and you can't slide off skinny sides and have the saddle ride up into your nerves. The only thing we hate about it is something that might not matter to you: It lacks saddlebag loops. Brooks puts those on 99 percent of its saddles, even narrow racing ones, so why they left them off this wideboy is the question of the decade.  Fortunately, you can buy add-on loops that bolt onto the rails and let you strap a bag there. I/Grant have that rig exactly on my Atlantis, and it works great. Mine are these. No, I didn't get a deal. I paid the same as normal people.

If you sit upright and a B.17 isn't wide enough and you won't ride a B.67 leather, get the C67 cambium. 

Length: 268 mm

Width: 200 mm

Height: 59 mm