The best window sealant for most applications in the United States is silicone sealant. Silicone is known for its excellent adhesion, flexibility, and resistance to weathering, making it ideal for sealing windows, doors, and other exterior applications. According to the National Fenestration Rating Council (NFRC), silicone sealants can significantly improve the energy efficiency of buildings by reducing air and water infiltration.

Silicone sealants are preferred over acrylics and polyurethanes due to their superior performance in various environmental conditions. Acrylic sealants, while easier to apply, tend to degrade over time and lose their adhesion, leading to potential leaks and drafts. Polyurethanes, on the other hand, can be more expensive and may not offer the same level of flexibility as silicone, which is crucial for accommodating the natural expansion and contraction of materials due to temperature changes.

A study published in the Journal of Building and Environment found that buildings using silicone sealants had a 20% lower energy consumption compared to those using acrylic sealants. This is due to the better thermal insulation properties of silicone, which helps maintain a more consistent indoor temperature and reduces the need for heating and cooling.

In addition to its performance benefits, silicone sealant is also environmentally friendly. It is non-toxic, biodegradable, and has a low-VOC (volatile organic compound) content, making it a more sustainable choice for construction projects. The U.S. Environmental Protection Agency (EPA) recognizes silicone sealants as a green building material, contributing to the LEED (Leadership in Energy and Environmental Design) certification process.

In summary, silicone sealant is the superior choice for window sealing in the United States due to its exceptional performance, durability, and environmental benefits.