Under which circumstance can't we use water soluble packaging ?

Water soluble film is made of polymer, polyvinyl alcohol. Like all polymer/plastic, it has its Tg. A glass transition temperature (Tg) is the temperature at which a polymer turns from a ductile material to a hard, brittle material. Each polymer with an amorphous structure has its own unique glass transition temperature, which makes a given polymer better suited for some applications over others. The PVA Tg is about 7-10 degree Celsius (44-50 degree Fahrenheit).. So during the cold season in the U.S., the temperature of storage and using should be much lower than such Tg.