I Changed Cotton Wick Brands and the Flame Is Now Larger — What Differences Between Supposedly Similar Wicks Could Explain It?

What can make one cotton wick burn taller than another

Flame size in a container candle is mostly a fuel-supply story. The wick draws melted wax and fragrance up by capillary action; the flame burns whatever arrives. If more arrives each minute, the flame grows, delivers more heat to the pool, deepens it, warms the glass and uses the candle up faster. So when you swap one cotton wick for another cotton wick and the flame is larger, the likeliest explanation is that the new wick moves more fuel — and the useful work is finding out which construction difference is responsible, because that tells you what to ask for next.

"Cotton" and "braided" describe a family, not a specification. Within that family, wicks commonly differ in braid pattern and tightness, ply count, the exact fibre or blend, whether and how they are primed, whether there is a core, any treatment applied to control burn, and the height of wick left above the tab. Here are the differences that can plausibly produce a larger flame, what each one tends to look like in a burning candle, and how to check it.

The last row is not a construction difference at all, and it is the first thing to rule out. The clue column is useful because the causes leave different fingerprints: a braid that carries more fuel gives a taller flame all the way through the burn; a taller neck or a long untrimmed tip gives a big flame early that settles; a wick that does not curl keeps a long upright tip that you can see at the one-hour check. The same-length, same-thickness post covers the bench checks for braid, priming and core in detail.

Rule out the three causes that are not the wick

Before you spend twelve candles on a diagnosis, make sure the comparison you already made was fair. Three things commonly make a new wick look bigger when it is not.

Measuring a flame so the numbers mean something

Flame height is the line that started this question, so it deserves a consistent method. CSI publishes no numeric flame-height limit, and this page does not invent one — you are comparing the new wick against your approved control, not against a number. What matters is that you measure both the same way every time.

Do the same for pool depth (a bamboo skewer marked in centimetres, dipped at the centre), jar-side heat (a thermometer reading or a consistent touch check at the same spot, a third of the way down the glass) and weight lost per hour. Those three lines tell you whether a taller flame is also delivering more heat — which is what makes it a safety question rather than a cosmetic one.

The 2 × 2 isolation test

Once trim, draught and set are controlled, one question remains: is the new wick bigger on its own, or only bigger with this fragrance? The answer changes what you do next, and a simple 2 × 2 design answers it. Pour twelve candles from one wax melt: six scented at your normal load, six unscented. In each set, three get the old wick and three the new.

Read the result like this. If the flame is taller in B than A and taller in D than C by a similar margin, the new wick is simply a heavier wick in your system: it delivers more fuel regardless of fragrance. If it is taller in B than A but not in D than C, the new wick reacts differently with this particular oil — fragrance components can change how fuel travels up a wick and how the tip burns, and two wicks can respond differently to the same oil. That second result matters commercially, because it means the new wick needs to be checked with every fragrance it will meet, which is the subject of the lavender-versus-vanilla post and the eight-fragrances post.

Pour and cure as your recipe already specifies. For Luxury Soy Wax CSI 464, CSI's guidance for melting and pouring is 80–90°C — confirm it on the product page. At 8%, each scented 200 g candle holds 16 g of Roasted Coffee and 184 g of wax; CSI 464 is rated by the wax maker up to 10% fragrance load, so the 16 g is inside the 20 g maximum. Each unscented candle is 200 g of wax. Burn in cycles of about 3–4 hours with full cool-down between them (a commonly used cycle, a working practice), three burns to screen, then carry boxes A and B through to the end of the candle.

What to retest after a cotton-to-cotton swap

Notice that flame height is a REPEAT line even though you have already seen the answer. The first observation told you something is different. It did not tell you how much, under a fixed trim, at which point in the candle, or whether it comes with more heat and soot. The NEW line appears only if the 2 × 2 test shows an oil-specific effect: that is a test you did not need with the old wick, because your old wick was approved with this oil. For the full combustion list in one place, see the wick-change retest checklist.

Scoring sheet for the four boxes

The acceptance column only uses A and B, because they are the candles a customer would actually light. C and D are there to explain the result, not to excuse it. The safety rule is the same throughout this series: no worse than your approved control on every safety line, and within your jar supplier's guidance and the candle fire-safety standard you work to (ASTM F2417 is a commonly cited US standard; we quote no numbers from it). A taller flame in B than in A is, by definition, a worse result on a safety line.

What to do with the result

Three tempting fixes are worth ruling out plainly. Printing "trim to 5 mm" on the label does not fix a heavier wick: many customers do not trim, and your candle has to be acceptable in their hands, not only in yours. Lowering the fragrance load to calm the flame changes the formula to suit a wick you did not want, and loses the throw you approved. Keeping it because the throw improved trades heat for scent — the better-throw, hotter-jar post explains why that trade is never worth it. The honest fix is a lighter wick, found by testing.

The priced test kit

The full 2 × 2 kit below makes twelve 200 g candles — six scented with Roasted Coffee Fragrance Oil at 8%, six unscented — in Luxury Soy Wax CSI 464, with a 5% pour-loss allowance (a labelled working assumption). If you only need the release decision and not the explanation, the scented pair (boxes A and B) costs ₹2,078.62; the diagnosis adds ₹861.40 of wax and jars. Use your own production wax and oil if they differ from ours.

The old wicks for boxes A and C are yours — six of them, which is why it is worth keeping a labelled bag of the previous wick whenever you change. Labour, electricity and time are not included; cost them from your own figures if you wish. Roasted Coffee is bought as 100 g + 15 g (₹483.22): at ₹3.90 a gram the 100 g bottle is well below the 15 g's ₹6.21, so two 50 g bottles (₹4.60 a gram) would cost more for the same test.

Releasing — or not — and writing it down

If the new wick passes A versus B on every line through to the end of the candle, release it the way the hub describes: update the recipe card with the full wick description, write the change record, check one candle from the first production batch against a control, and keep retained wicks and a retained candle. If it fails, the record is just as useful. Note which box pattern you saw — heavier overall, or oil-specific — because that tells your next supplier exactly what you need: "a lighter cotton wick than this one" or "a wick that behaves the same with coffee as with plain wax".

If the new wick also mushrooms more, that usually travels with the bigger flame — the mushrooming post explains why a matching melt pool does not make it equivalent. If the 2 × 2 test shows the new wick is simply heavier, treat any decision to keep it as a size-up and run the late-burn checks in the one-size-up post. And if an order is due before you can finish the full test, the emergency 1,000-candle post sets out the smallest defensible check.

Frequently asked questions