Wick types
Updated
Wicks come in series, and a series is a design rather than a dimension. Changing series is a bigger change than changing size.
Series, not sizes
CD, ECO, LX, HTP, CDN, zinc-core, wooden. Each is a construction with its own burn characteristics, and each has its own numbering that does not translate to another's.
A "CD 12" and an "ECO 12" are not comparable, and a conversion chart between series is a starting point for a test rather than a substitute for one.
Flat and square braid
The traditional constructions. Flat braid curls as it burns, which self-trims the tip and keeps carbon down.
They suit softer waxes and are common in soy containers. They are also the ones most likely to lean if they are not centerd well.
Cored wicks
A braid around a core that holds the wick upright. Paper and cotton cores are the usual ones.
They stand straight in a deep melt pool, which is their advantage, and they can burn hotter, which is their cost.
Zinc cores still exist. Lead cores do not: metal-cored wicks above 0.06 percent lead by weight of the core, and candles made with them, have been banned since October 2003. Buying from a reputable supplier is how you stay clear of it, and there is a labeling consequence if you use metal-cored wicks at all.
Wood
A flat wooden wick that crackles. Distinctive, popular, and a different craft: wood needs a wider, shallower melt pool and is sized by width rather than by a series number.
It is also less forgiving. A wood wick that will not stay lit is a common complaint and it is usually a wax or load problem rather than a wick fault, which makes it harder to diagnose.