The hairline is the finest part of a letter’s outline. Inherited from pen writing, where the pressure and angle of the tool varied the thickness of the stroke, it stands in contrast to the thick stroke, the heaviest part.
Where to see it
Hairlines are visible on the thin parts of letters, such as the horizontal bar of “A” or “H”, the top and bottom of “o”, the connecting strokes of “n” or “m”, or the thin diagonals of “V” and “W” in high-contrast typefaces.
Why this detail matters
The design of hairlines directly shapes the contrast and personality of a typeface:
- Very fine hairlines set against heavy thick strokes create a strong contrast that defines Didones such as Bodoni or Didot and gives them great elegance;
- Hairlines close to the thickness of the thick strokes produce a more uniform, sturdier design, typical of many sans serifs;
- At small sizes or on screen, hairlines that are too fine can disappear, so their thickness must be designed with the font’s intended use in mind.
Related term
The thick stroke is the heaviest part of a letter’s outline; the difference between thick strokes and hairlines defines a typeface’s contrast.
Anatomy glossary
Ascender, Descender, Sidebearing, Joint, Axis, Bar, Beak, Bowl, Loop, Set width, Counter, Serif, Stem, Leg, Minim, Baseline, Eye, Belly, Foot, Point, Tail, Cross stroke, Terminal; X-height, X-height, Cap height, Body; Mean line, Ear, Spur, Ball terminal, Ligature, Apex, Vertex, Arm, Shoulder, Spine, Em dash, Thick stroke, Hairline, Bracket, Bounding box