Seeding with ice nuclei, such as silver iodide particles, or with very cold materials, such as dry ice pellets or liquid propane, can supply some clouds with additional ice particles and thus increase the efficiency of the cold-cloud process.
The silver iodide is usually released from devices called liquid fuel generators, or pyrotechnic flares, which can produce as many as 1,000,000,000,000,000 particles from 1 gram of silver iodide. The nucleating ability of silver iodide increases as the temperature falls and varies with the type of device used.