The most popular digital materials are Vero White Plus and Tango Black plus which let you dial the shore hardness of parts, from 27A to 95A. This technology also allows parts to have a multitude of durometers allowing clients to simulate over molded prototype parts without having to do any post assembly.
The family of Tango materials (TangoGray™, TangoBlack™, TangoPlus™ and TangoBlackPlus™) boast various levels of elastomer characteristics: Their Shore Scale A hardness, elongation at break, tensile strength and tear resistance make them suitable for a wide range of 3D printing applications, such as rubber contours and overmolding, soft-touch coatings, knobs, grips, handles, gaskets, and footwear.
Axis Prototypes is a great supplier to work with. They provided more than enough information to make an informed decision on alternatives.