I thought "Only a SITH deals in absolutes".:behave
Yeah I was absolutely going to ditch them last night :lol
When you say "specify", are you referring to a specific service that provides this kind of material and work?
As mentioned, once you find a supplier (I used ERA products) you will be able to inspect samples of the cured product and feel the hardness. I chose OC80A based on the feel of the sample for the outer-sole. For a mid sole, I would suggest OC25A.
I've been looking at silicone molds but the only problem is the sculpting of the soles. If I remember correctly, Cloneprops had a 3D model of his parts made up first and then made molds from these. I've never attempted 3D modeling and i'm unsure of the cost. The only thing I could do is have someone make the CAD files for me for a fee or sculpt all the parts out of another material by hand and then mold those.
And your uppers are already looking great, a small rethink can only get better.
I am working on a 3D model for the mid-soles. Just $$$ that I don't want to spend if I don't have to.
The easiest way to make these is:
1. Have a template cut from at least 3 layers 16mm MDF. If you wanted the recessed parts for the outer-sole, then you laser cut a 2nd profile using 3mm MDF and glue that in place to create a new 3D shape. At this stage, you would also be able to add the recesses for the side parts.
2. Invert the mid-sole and then raise it up by at least 40mm and Vac Form the shape. This works because the widest part is the top (which is inverted).
3. You then trim the top side into shape.
4. Lay the original MDF part into the base and using bondo, create the arch and build up the wall.
Presto! You now have a solid flat mid-sole that you can cast.