How does Duo work?

A blue dye housed in a blister is held adjacent to a micro-porous membrane. Upon squeezing the activation button the liquid dye comes out of the blister and into contact with the membrane.
If the temperature of the product is below the stated ‘STOP’ temperature, the blue dye changes state to solid form, and it is unable to move through the membrane. If the temperature rises to or above the threshold temperature, the dye changes to liquid form and moves at a precise rate through the membrane. Its progress is irreversible and the distance it travels through the viewing window indicates the cumulative time the indicator has been exposed to the threshold temperature or above.
The 10°C and 34°C threshold indicators use different liquid dyes which melt and solidify at different temperatures. The liquid dye in the 10°C blister has a STOP of 8°C/46°F and the liquid dye in the 34°C blister has a STOP of 30°C/86°F.

adminHow does Duo work?