Question: is caulk made of silicone?
Answer: Pure, or 100%, silicone is the premium caulk for jobs exposed to water. Silicone caulk is expensive but worth the cost due to its flexibility and long life. Most formulas are mildew-resistant and have inhibitors to slow discoloration (but all caulk gets ugly over time). The only big downside is that it's not paintable.