Lash science · The natural lash
The physics of a lash
Every lash is a small piece of engineering. Its length manages the air in front of your eye, its curve throws off water, and its thickness decides how much it can carry. Those three facts set the rules for every set we apply.
Length
One third of the eye
In 2015 a team at Georgia Tech measured the lashes of 22 species of mammals. In every one, the lashes were about one third as long as the eye is wide.1
They then put a model eye in a wind tunnel. At that length, lashes halved the evaporation of the tear film and the dust reaching the eye. Shorter lashes shelter less. Longer lashes do something worse: they act as a funnel and carry the air down onto the eye.1
Sheltered. A pocket of still air sits over the eye: about half the evaporation, about half the dust.
Air meeting the eye head-on, seen in cross-section. A drawing of the mechanism the study describes, not its data.
At the atelier
We measure the width of your eye before we choose a length. The longest fibres go where your eye can carry them, and the set as a whole stays close to its natural proportion. For more drama we change the curl, the density and the map before we add length.
Length, in the libraryA pocket of still air, held in place by a row of hairs.
It is in front of your eye now.
Curve
Built to throw off water
A lash repels water, and its surface is covered in scales that overlap like roof shingles, all pointing to the tip. Water travels easily from root to tip and hardly at all the other way.2
The curve does the rest. In 2024 researchers at the Chinese Academy of Sciences found that a lash bends close to the brachistochrone, the curve down which a drop falls fastest.2
Between the same two points, a drop on a straight line takes about 18 percent longer than a drop on that curve.6
At the atelier
An extension continues the lash's own line. We choose the curl from the angle your natural lash already grows at, so the base of the fibre lies flat along it and the bond holds.
Curl, in the libraryTwo drops released together, one on the curve of a lash and one on a straight line between the same points.
The surface of a lash, enlarged: scales overlap toward the tip, so water moves one way.
Structure
What a lash is made of
Under a microscope, a lash is three parts that fit inside one another.3
A lash cut across. Choose a layer.
Several layers of flat cells, sealed tight. It keeps water out and protects what is inside.
90 to 160
lashes on the upper lid, in five or six rows
75 to 80
lashes on the lower lid, in three or four rows
0.12 to 0.14 mm
of growth a day
4 to 10 weeks
of growth, in a life of 4 to 11 months
12 mm
the length a lash rarely passes
No muscle
a lash cannot move itself, unlike the hair on your arm
Figures from source 3.
Lashes also differ from person to person. In a study of 4,661 lashes, thickness, number and the angle of lift all varied between groups of women. Length and growth rate did not.4
At the atelier
Every lash is on its own clock, so a set sheds a few fibres a day with the lashes that carry them. That is the reason for a fill every two to three weeks, and the reason we never bond two lashes together.
Retention and fills, in the libraryLoad
Thickness matters more than length
A lash is a beam fixed at one end, and an extension is a weight added along it. Two rules from first-year mechanics decide the rest.6
The weight of a fibre grows with the square of its diameter. Double the diameter and it weighs four times as much. Add two millimetres to a ten millimetre fibre and it weighs a fifth more.6
The stiffness of the natural lash grows with the fourth power of its diameter. A lash twice as thick is sixteen times harder to bend, which is why a fine lash and a strong lash cannot carry the same set.6
At the atelier
This is the arithmetic behind volume work. A hand-made fan of four 0.07 mm fibres is lighter than one 0.15 mm classic fibre, and it covers far more of the lash line. We choose the diameter from the lash that has to carry it.
Thickness and weight, in the libraryChoose a fibre diameter
4.6 fibres of 0.07 mm weigh the same as one classic fibre.
Fibres of the same length and material. Real fibres taper to a point, so each weighs less than a plain cylinder, and the ratios stay close.
Beauty
Beauty follows the same number
In 2023 two psychologists showed people faces whose lashes ran from none at all to half the width of the eye, and asked how attractive each one was.5
The answer rose and then fell. It peaked close to one third of the eye's width: about a quarter for some faces, up to two fifths for others.5
The length people prefer and the length that shelters the eye best are nearly the same number. The authors suggest we read that proportion as a sign of health. That part is a hypothesis. The preference is the measurement.5
The shape of the result, redrawn. The faces were computer generated and rated online.
At the atelier
Three measurements before any set
A free 30-minute consultation comes first. We look at your natural lashes under magnification and draw the map before a single fibre is placed.
- Length
- from the width of your eye
- Curl
- from the angle of your own lash
- Weight
- from the lash that has to carry it
Sources
Every numbered line above comes from one of these. Where a claim is still a hypothesis, the text says so.
- 1Eyelashes divert airflow to protect the eyeAmador, Mao, DeMercurio, Montero, Clewis, Alexeev and Hu. Journal of the Royal Society Interface, 2015.Measured: 22 species and a wind tunnel
- 2Rapid water drainage on human eyelashes of a hydrophobic Brachistochrone fiber arrayZhou, Chen, Cheng, Gao, He, Wang, Jiang, Dai and Dong. Science Advances, 2024.Measured in the laboratory
- 3The eyelash follicle features and anomalies: a reviewAumond and Bitton. Journal of Optometry, 2018.Review of the published research
- 4Ethnic characteristics of eyelashes: a comparative analysis in Asian and Caucasian femalesNa, Kwon, Kim, Park, Oh, Kim, Cho and Eun. British Journal of Dermatology, 2006.Measured: 4,661 lashes on 30 women
- 5Eyelash length attractiveness across ethnicitiesPazhoohi and Kingstone. Scientific Reports, 2023.One study: computer-generated faces, rated online
- 6The weight of a round fibre, the stiffness of a round beam, and the curve of fastest descentTextbook mechanics. Our own arithmetic, shown in the text.Standard physics, applied by us
Lash science
The natural lash
- Anatomy and the growth cycleRead
- Chemistry: keratin, bonds, pigmentRead
- Physics: length, curve, structure, loadThis chapter
- Evolution and functionRead
- Psychology and the perception of beautyRead
- Health: keeping and improving natural lashesRead