Tunneling is when the wick burns straight down the center of a candle without creating a full melt pool. 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 ECO 12 with the 464 soy wax in an 8 oz tin and saw tunneling, you would next want to test the ECO 14.
Our guide on How to Conduct a Basic Burn Test will be useful as you test different wicks!