Tunneling is when the wick burns straight down the center of a candle without creating a full melt pool within 2 hours of being lit. Tunneling is typically an indication that the wick is not large enough for your wax, container, fragrance, dye combination. Depending on how much wax you have left on the sides of your container, you may need to go up one or even two sizes in the wick series you are using. For example: if you used the CD 16 with the 464 soy wax in an 8 oz tin and saw tunneling, you would next want to test the CD 18.
Our guide on How to Conduct a Basic Burn Test will also be useful as you test different wicks!