  We have designed, fabricated and characterized absorptive thermal blocking
filters for cryogenic microwave applications. The transmission line filter's
input characteristic impedance is designed to match $50\,\Omega$ and its
response has been validated from 0-to-50\,GHz. The observed return loss in the
0-to-20\,GHz design band is greater than $20\,$dB and shows graceful
degradation with frequency. Design considerations and equations are provided
that enable this approach to be scaled and modified for use in other
applications.
