NIST provides a completely free introductory version called mini-REFPROP 10.0 .

NIST does offer REFPROP 10 as freeware. The common myth of a “free 2021 version” stems from:

REFPROP (NIST Standard Reference Database 23) offers thermophysical properties of pure fluids and mixtures. Version 10 (released in 2018 and updated through 2021) supports over 147 pure fluids and includes:

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However, engineers, researchers, and students can legally access REFPROP 10’s calculation capabilities through legitimate, low-cost official channels, limited free student versions, or highly accurate open-source alternatives. What is NIST REFPROP 10?

Calculations run significantly faster, making it highly efficient when linked to external simulation routines.

(Note: This write-up does not provide or link to unauthorized downloads.)