These are by far the best molds I have ever used. The bottom is concave so you have a wax well built into the top of the candle but you also have plenty of room for putty AND I use HVAC DUCT Tape (it is like aluminum foil) and never have leaks. The previous poster gave a one star because she didn't have putty. A novice mistake which has absolutely nothing to do with these molds. They are perfect - no seam - I don't clean them I just reuse them. They do not require silicone spray and my candles slide right out of these fabulous molds. Well worth the money! Will last years with heavy use. I love them and so do my customers who buy my candles.