The Kryolan® cold foam instruction sheet suggests working in a room temperature of at least 80°F (about 27°C). That might be a bit warm, but colder room and mold temperatures can cause the foam to fail occasionally. High humidity can also cause foam to fail; ambient room humidity and even wooden stir sticks with any moisture can cause the foam to collapse. Stone molds or plaster molds must be clean and thoroughly dried before using. New molds can be oven-dried for several hours at about 200°F (93°C); air-drying molds can take as long as several days.
Sometimes it is possible to reconstitute a collapsed piece by carefully crushing it; you will hear a popping sound like the noise when you crumple and twist bubble wrap. What you are doing is popping cells in the urethane, allowing the foam to return to its molded shape. Sometimes this will work, sometimes it won’t.
The shelf life of cold foam is limited once the product containers have been opened. The chemicals are affected by exposure to air and light; therefore, the components should be stored in a cool, dry, dark area and used fairly soon after purchase. Keep the containers tightly sealed after each use. The manufacturer’s recommended shelf life is six months after manufacturing, but I’ve made excellent pieces with foam components much older than that.