  Controlling stray light at millimeter wavelengths requires special optical
design and selection of absorptive materials that should be compatible with
cryogenic operating environments. While a wide selection of absorptive
materials exists, these typically exhibit high indices of refraction and
reflect/scatter a significant fraction of light before absorption. For many
lower index materials such as commercial microwave absorbers, their
applications in cryogenic environments are challenging. In this paper, we
present a new tool to control stray light: metamaterial microwave absorber
tiles. These tiles comprise an outer metamaterial layer that approximates a
lossy gradient index anti-reflection coating. They are fabricated via injection
molding commercially available carbon-loaded polyurethane (25\% by mass). The
injection molding technology enables mass production at low cost. The design of
these tiles is presented, along with thermal tests to 1 K. Room temperature
optical measurements verify their control of reflectance to less than 1\% up to
65$\circ$ angles of incidence, and control of wide angle scattering below
0.01\%. The dielectric properties of the bulk carbon-loaded material used in
the tiles is also measured at different temperatures, confirming that the
material maintains similar dielectric properties down to 3 K.
