Silicone and polyurethane are choices for exterior caulking, but they do not perform the same way in every building area. How Silicone Handles Cold WeatherSilicone stays flexible across a wide temperature range, which is a major advantage during Ottawa winters. However, standard silicone usually cannot be painted. Old caulking often needs removal so the new product can bond to a sound surface. Experienced caulking contractors may use both products on the same building because each area has different requirements.