Type I vs Type IV Deicing Fluid: What's the Difference?

What does Type I fluid do?

Type I is the deicing fluid. It is applied heated and usually diluted with water, and the heat does much of the work of melting contamination. Because it isn't thickened, it flows off quickly and sheds at low speeds, which makes it compatible with a wide range of aircraft, from Cessna singles to Citations.

The trade-off is short protection: when Type I fails, it fails quickly. The FAA's Type I holdover tables only apply to heated Type I fluid.

What does Type IV fluid do?

Type IV is an anti-icing fluid. Thickening agents make it cling to wings and tail surfaces as a protective layer, giving it the longest holdover times of the standard fluid types.

In North America it is typically applied cold, after the aircraft has already been deiced. It is designed to shear off during the takeoff roll on aircraft with rotation speeds above roughly 100 knots, which is why it suits jets and faster turboprops.

Deicing vs anti-icing: one-step and two-step

Deicing removes contamination that's already there. Anti-icing protects a clean surface from new precipitation.

A one-step procedure uses a single heated fluid application for both. A two-step procedure deices first with Type I, then anti-ices with a thickened fluid, which is common when snow or freezing precipitation is still falling and taxi times are long.

What about Type II and Type III?

Type II is thickened like Type IV, is generally clear, and offers shorter holdover times than Type IV; its use has declined in favor of Type IV. Type III, generally bright yellow, falls between Type I and Type II/IV in thickness and was formulated for aircraft with rotation speeds of 60 knots or higher.

Many piston singles rotate well below 100 knots, so thickened fluids generally aren't a fit. The AFM/POH is the final word.

Fluid isn't the only option: heat (hangar) deicing

Heat deicing means moving the aircraft into a heated hangar and letting snow, ice, and frost melt off without any fluid. It works well for heavy accumulation and for owners who'd rather keep glycol off the airframe.

The key is drying: melted water can refreeze in control surface hinges, gaps, and wheel wells once the aircraft goes back into the cold, so surfaces should be fully dry before departure. Heat deicing leaves no protective fluid behind, so if precipitation is still falling, eligible aircraft may still need Type IV anti-icing before departure.

Holdover time: why the clock matters

Holdover time is the estimated window a fluid protects the aircraft against freezing precipitation. It depends on fluid type, concentration, outside air temperature, and precipitation type and intensity.

The FAA publishes new Holdover Time Guidelines every season; the Winter 2026–2027 guidelines were issued August 11, 2026. The clock starts at the beginning of the final fluid application.

Before takeoff, critical surfaces must be free of adhering frost, ice, and snow: the FAA's clean aircraft concept. Small-aircraft operators should also review FAA Advisory Circular 135-17, Pilot Guide: Small Aircraft Ground Deicing.

Who should take a closer look

• Jet and turboprop crews planning winter trips into Metro Detroit, where two-step Type I and Type IV deicing and holdover planning come up often.
• Charter operators who need predictable winter departure times.
• Piston owners, especially Cessna and Piper operators, who often get the most benefit from heat deicing or a heated hangar night instead of fluid, and who should confirm approved fluids in their POH.

At Michigan Aviation, we offer every option at KPTK: heat deicing, Type I fluid deicing, and Type IV anti-icing, plus heated hangar space that keeps the airplane clean before it ever reaches the ramp.