R290 is pure propane: the same substance as bottled gas, but in refrigeration grade (99.5%). Its thermodynamic properties are very good; it gives 10–15% higher efficiency than R404A, its pressures are close to R22, it is compatible with mineral and POE oils, it does not affect the ozone layer and its GWP is 3. This is why it is one of the key refrigerants of the post-F-gas era.
Its one big obstacle is flammability (safety class A3). For this reason the standards limit the charge: up to 500 g is common in hermetic commercial appliances (cabinets, ice machines, small monoblocks), and the 2024 standard updates allow higher charges under certain conditions. Large-charge systems need an ATEX-compliant machine room, gas detection and ventilation.
In practice R290 is spreading fast in supermarket cabinets, plug-in monoblocks, small chillers and heat pumps; in large cold storage warehouses it is generally used with a glycol or CO₂ secondary circuit (R290 chiller in the machine room, glycol in the cold room). It should be serviced only by technicians trained in flammable refrigerants.