How can candle wicks hold a flame for so long?

Q: How can candle wicks hold a flame for so long?

– Sadhika G.

A: A candle wick holds a flame because it isn’t just a string that burns. Its main purpose is to deliver fuel to the part of it that’s very hot.

When you light the wick, the heat quickly melts the wax near its base. The wick is made of cotton fibres woven tightly together, and they together serve as ‘tubes’. Through capillary action, they draw the liquid wax upwards against gravity, just as a paper towel suspended over a bucket of water will absorb it upwards.

Near the flame, the liquid wax gets hotter and turns into vapour. And it’s the wax vapour rather than the solid or liquid wax that actually burns. As long as the wick can keep supplying vapour at roughly the same rate the flame consumes it, the flame will be steady.

The wick itself chars slowly. Good wicks are designed to curl over as they burn, moving the tip into the hottest part of the flame. There, the excess wick turns to ash and breaks off, so it doesn’t grow too long and produce smoke. This is how a candle keeps a flame alive for many hours.