The market’s type taxonomy distinguishes five fluid families that shape product development and pricing. Organic fluids—principally silicone‑based and glycol‑based formulations—provide superior thermal stability and low toxicity, commanding the largest share (≈40 %) due to their versatility across high‑temperature power and chemical uses. Inorganic fluids, such as molten salts and liquid metals, deliver exceptional heat‑capacity at temperatures exceeding 600 °C, yet their niche applications in concentrated solar power and advanced metallurgy limit their market to about 15 %. Nanofluids, engineered by suspending nanoparticles in carrier liquids, offer enhanced conductivity and are emerging in electronics cooling, currently representing roughly 8 % of sales. Synthetic oil derivatives, including ester‑based and phosphate‑based fluids, balance high flash points with moderate viscosity, supporting roughly 22 % of the market, especially in HVAC and automotive thermal management. Water‑based fluids, the most environmentally benign option, occupy the remaining 15 % and are prevalent in food‑processing and low‑temperature HVAC circuits. The relative revenue contribution of each type reflects performance‑cost trade‑offs that define the Heat‑transfer Fluids market structure.