Specific heat capacity (Cp) is the amount of heat required to raise the temperature of a unit mass by one degree at constant pressure. For Skydrol it is measured in kJ/(kg·K) [SI] or Btu/(lbm·°F) [Imperial], and governs sizing of heat exchangers and thermal management systems in the hydraulic circuit. The heat transfer equation is:

Q = ṁ × Cp × ΔT

where Q is heat flow (W or BTU/hr), ṁ is mass flow rate, and ΔT is the temperature difference across the heat exchanger or system boundary.

Specific heat values for all four Skydrol grades are published in Eastman's Skydrol product comparison brochure (Publication EASAF7870), tested per ASTM D2766. Each grade was measured at only two or three temperatures — 38 °C, 93 °C, 120 °C, and 149 °C depending on the grade — so the calculator on this page linearly interpolates between those published points rather than fitting a curve. No extrapolation is performed: inputs outside a grade's own tested range return "Out of Range."

Cp increases with temperature for all four grades, consistent with typical hydraulic fluid behavior. Skydrol PE-5 has the highest specific heat of the four grades at a given temperature; Skydrol 5 has the lowest.

Skydrol PE-5 is the exception to watch on the chart: Eastman's brochure publishes only two Cp points for it (38 °C and 120 °C, versus three for the other grades up to 149 °C), so its line is shown dashed, is nearly flat over that narrow interval, and stops short of 300 °F. This is a genuine gap in the published data, not a digitization error — no 93 °C or 149 °C value for PE-5 has been published.