There are several general types of polymer used to manufacture most high-performance caulks: silicones, polyurethanes, latex-acrylics, and solvent-based “block copolymer” synthetic rubbers (which include butyl as well as some of the newer proprietary synthetic formulations).

The best type of caulk for the job depends largely on the materials to which the caulk must bond. For bonding dissimilar materials (for example, wood to masonry), look for sealant that can handle a lot of joint movement.

For the most part, polyurethane caulks provide the best all-around performance for exterior applications, but they are more expensive than most other caulks and can be difficult to clean up (below).

Type Maximum Joint Movement Life Expectancy Comments
Silicone 50% 20 years Most flexible. Can be applied over the widest range of temperatures but doesn't stick well to wet surfaces or masonry; generally not paintable (though paintable products are available).
Modified Silicone Polymer Combines the properties of polyurethane, silicone, and acrylic; easy to work with.
Polyurethane 25% 20-30 years Good all-purpose caulk; excellent adhesion to most materials; difficult to clean up; paintable.
Polysulfide 12-25% 10-20 years Difficult to handle; used mostly for sealing joints in concrete; may require primer on porous surfaces; wear gloves and maintain ventilation during application.
Acrylic Latex 2% 10-20 years interior only Interior use only; easy to work with; cleans up with water.
Siliconized Acrylic Latex 25% 20-30 years The addition of silicone makes this more flexible and water-resistant than standard acrylic latex; easy to work with and cleans up with water.
Butyl Rubber 5-10% 5-10 years Poor adhesion on damp surfaces; attracts dirt; difficult to handle.
Synthetic Rubber 50% 5-20 years Variety of proprietary formulas available; very flexible; can be applied in wet and cold weather; paintable.
Oil Based 1-2% 3-5 years interior;
1-2 exterior
Not recommended.
Ethylene Copolymer 25% 10-20 years Reasonable adhesion to most materials; can be painted.

The table is meant only as a rough guide to help you narrow choices. (For instance, life expectancy and joint movement vary with the particular product.) While some caulks and sealants fit neatly into these broad categories, others, such as paintable silicone, are variations. There are also hybrid and specialty caulks with proprietary formulas that combine the properties of two or more types. As always, consult the manufacturer's specs on any particular product you are considering.

To learn more about exterior caulks and sealants, visit the JLC Field Guide.