What ATP class IR and k ≤ 0.40 W/m²K mean

ATP splits insulation by the k coefficient: at most 0.70 for IN and 0.40 W/m²K for IR. IR is mandatory for the sub-zero refrigerated classes.

3 March 2026Updated 28 September 2026

Short answer

In ATP, IR is heavy insulation with a k coefficient of at most 0.40 W/m²K; normal insulation, IN, is limited to 0.70. The smaller k is, the less heat passes at the same temperature difference. The minus 10 and minus 20 degree classes require IR, so a quote for sub-zero transport with ice packs or eutectic plates should state IR.

The k coefficient is the heat power passing through one square metre of surface per degree of temperature difference, in W/m²K. Under Annex 1 of the ATP agreement, IN is normal insulation with k of at most 0.70. IR is heavy insulation with k of at most 0.40, and equipment wider than 2.50 m also needs side walls of at least 45 mm.

Refrigerated equipment class	Temperature	Insulation
A	at most +7 °C	IN is enough
D	at most 0 °C	IN is enough
B	at most -10 °C	IR required
C	at most -20 °C	IR required

0.40 is an upper limit, so a calculation that takes heat gain as k times outer surface area times the inside-outside temperature difference, using that limit, shows the worst case. GEBHARDT states that Isotec TBX containers are ATP and HACCP certified; request the model's ATP document and k value from Aris Makina, and we obtain them from GEBHARDT and pass them on.