Silicone Vs. Polyurethane Caulk: What's the Difference?

In the world of sealants, caulk is a multipurpose tool. It is used in weatherization, plumbing, tiling and other projects in and around the home. Two materials used often in caulk tubes are silicone and polyurethane. Despite their common use and other similarities, there are some major differences between polyurethane caulk and silicone caulk that dictate their uses for household projects and others.

Primary Difference

In the world of sealants, caulk is a multipurpose tool. It is used in weatherization, plumbing, tiling and other projects in and around the home. Two materials used often in caulk tubes are silicone and polyurethane. Despite their common use and other similarities, there are some major differences between polyurethane caulk and silicone caulk that dictate their uses for household projects and others.

Speed

Silicon is best at drying quickly. Polyurethane remains wet or "tacky" for up to 24 hours after the silicon has dried, according to the Dow Corning Corporation. The use of silicone in a high traffic area is a mistake, however, because it does not hold up to abrasion as polyurethane does.

Material Bond Limits

Silicone is the best sealant for glass, tile and metal, while polyurethane works very well on natural products like wood. Silicone actually fails when applied to wood. Polyurethane succeeds with this material as well because it dries hard. The hard drying actually make polyurethane a lot more difficult to apply as it stiffens when out of the tube. Silicone has a much easier application. It cures soft and is therefore softer when being applied, according to Fine Home Building.

Weather Resistance

Silicone is the best sealant for the colder temperatures. The cold actually does not affect application. Polyurethane, however, becomes even harder to apply and does not make a permanent bond when the temperatures are very low. Silicone remains flexible unlike the polyurethane.

Roger Caffin, "FAQ: Silicone vs.Polyurethane vs. Acrylic Proofing," Bushwalking.org.
Brian Potililo, "Making Sense of Caulks and Sealants," Fine Homebuilding.