Because it is proprietary software, finding a legal "free" version—especially for version 9.1—requires understanding how NIST distributes its data and what legitimate alternatives exist. Understanding RefProp 9.1
It only includes a few fluids (like water, nitrogen, and R134a).
Many universities and large engineering firms hold site licenses. If you are a student or employee, check your organization's software portal. You may already have access to a legal download. 2. NIST Standard Reference Database refprop 91 free
If you cannot afford a RefProp license, there are powerful, open-source alternatives that offer similar accuracy for common fluids. ⚙️ CoolProp (Recommended) CoolProp is the best free alternative to RefProp. Completely free for all users.
A free, open-source chemical process simulator. It includes its own property packages and can integrate with CoolProp to provide RefProp-like functionality within a full plant simulation environment. A Note on "Free" Downloads Because it is proprietary software, finding a legal
Fees fund the continued updates of fluid property libraries. How to Get RefProp (The Right Way)
NIST invests heavily in experimental data collection. If you are a student or employee, check
RefProp (Reference Fluid Thermodynamic and Transport Properties) is a highly specialized program developed by the National Institute of Standards and Technology (NIST). It is the industry gold standard for calculating the physical properties of chemicals and refrigerant blends.
Excellent for students learning the interface or testing basic thermodynamic cycles. Legitimate Free Alternatives to RefProp
Specifically designed to target engineering workstations.