Caulk is a flexible material used to seal air leaks through cracks, gaps, or joints less than 1-quarter-inch wide between stationary building components and materials. For components that move — doors and operable windows, for example — weatherstripping is the appropriate material.
Before caulking air leaks in an existing home, you will need to detect the leaks and assess your ventilation needs to ensure adequate indoor air quality. In addition to sealing air leaks, caulking can also prevent water damage inside and outside of the home when applied around faucets, ceiling fixtures, water pipes, drains, bathtubs, and other plumbing fixtures.
For common caulking types and tips and tricks, Visit: http://energy.gov/energysaver/articles/caulking