Cryopreservation of coral sperm requires reliable, travel-ready, inexpensive hardware. To this end, we developed and tested a robust, second-generation, conduction-based cryovial cooling rack assembled from 3D-printed and commercially available parts. Cooling rates from -10 to -80 degrees C were found to be repeatable at -22.9 /- 1.9 (rate /- SD) degrees C/min for 1-mL samples and -35.4 /- 3.3 degrees C/min for 0.5-mL samples. This represents an improvement on the variability of cooling rates in an older design, which was found to be -31.8 /- 7.1 degrees C/min for 1-mL samples. Design files and a manual were produced to encourage widespread use and the development of derivative designs.
