 isn't paintable. Urethane is. Siliconized acrylic caulking is paintable also. So if you're going to paint it and you got mixed substrates, you definitely want to use the urethane. If you're going to just use white caulk or clear caulk, silicone is fine. Silicone is just a little bit less expensive than a urethane. That's why I bring that up.