Double shot ABS. DSS is the newly-revived profile made by Signature Plastics. Some might call DSS a sculpted version of DSA, as they are similar in many ways, including: thickness, spherical, textured top with smooth sides.
The base set will cover most, if not all, common 40% boards and numpads/macropads. Row profile is 2-3-4-3.
NOTE: R3 2.75u molds do not exist. The 2.75u spacebar is DSA.