Abstract: A thaw duration detector is provided by filling the bottom of an open ended heat sealable plastic pouch with a dilute aqueous indicator solution, freezing said indicator solution in the bottom of the pouch, positioning an absorbent strip having an indicator strip secured thereto at one end thereof within said pouch with the indicator strip near the open end of the pouch and the other end of the absorbent strip close to the frozen solution, and then heat sealing the pouch across the same to provide a first compartment in which the frozen aqueous solution is confined, and at least one further compartment containing the absorbent strip.