What is qmax?

qmax is the maximum heat flux, typically measured in W/cm². When skin comes into contact with fabric or material, heat rapidly flows from the skin to the material. This instantaneous maximum heat flow rate is qmax.

The higher the qmax, the cooler the sensation at the moment of contact.

qmax was proposed by Professor Kawabata of Kyoto University in the 1970s and is measured using KATO TECH's KES-F7 Thermo Labo. It is one of the earliest systems to quantify the sensation of coolness.

Why is qmax important?

In the past, coolness, comfort, and touch sensation were mostly judged subjectively by humans, which often led to inconsistencies. The value of qmax lies in:

1. Objectively evaluating the cooling performance of materials

2. Comparing the cooling differences between different products

3. Establishing product development targets

4. Benchmarking against competitor products

5. Assisting in the development of cooling textiles, sportswear, underwear, cooling pads, and other products

qmax values under different testing conditions cannot be directly compared.

The temperature difference condition, especially ΔT (delta T), is very critical. ΔT is the temperature difference between the sample surface and the heat flow plate. The greater the temperature difference, the greater the heat flow, and the higher the qmax will be.

On the surface, B appears cooler, but because B was measured at a higher ΔT, they cannot be directly compared. If converted to the same ΔT = 10°C, B's qmax would become 1.00, making A actually cooler.

Different standards have different ΔT conditions.

qmax is not everything about coolness

qmax only represents the coolness at the moment of contact, not the overall wearing comfort.

It cannot fully reflect:

• Sustained/Prolonged coolness
• Moisture wicking
• Breathability
• Non-stickiness to the skin
• Overall tactile comfort

Therefore, when evaluating cooling fabrics, you cannot rely solely on qmax; you need to assess it together with other performance characteristics.

Application Industries

KATO TECH's Main Cool feel Testing Instruments: