Eyelash Extension Products in Depth

Course: Eyelash extensions course from A to Z · Module 4 of 10

In Module 2 you set up your workstation; now it’s time to really understand your eyelash extension products: curls, diameters and lengths, what “mink” and “silk” fibres are actually made of, how cyanoacrylate adhesive works and why humidity changes everything, and the role of primers and removers.

Module objectives

Read curl types (J, B, C, CC, D, L, M and their variants) and know when each makes sense.
Choose suitable diameters and lengths for the technique and the natural lash.
Know what extension fibres are made of and what the trade names mean.
Understand the basic chemistry of cyanoacrylate adhesive and how humidity and temperature affect it.
Know what primers and the different types of remover are for, and the precautions they need.

Eyelash extension products: the lashes

Every extension is defined by three parameters: curl, diameter and length. On a tray you’ll typically see them written as, for example, “C 0.10 11 mm”.

Curls

Curls are named with letters, but they are not standardised between brands: one manufacturer’s C can look like another’s CC. Always compare your supplier’s curl chart. As a rough guide, industry sources describe them like this:

Curl	General description	Typical use
J	The straightest; some brands call it A	Very natural look, lashes that already grow upwards
B	Soft curve	Natural results on lashes that already point upwards
C	Medium curve	The most versatile; suits almost every case
CC	Between C and D	A bit more lift than C
D	Strong curve	A more open, dramatic look
C+ / D+	Slightly curlier versions of C or D	Fine-tuning between curls
L (and variants such as LC, LD, L+)	Flat base with a sharp upward lift, L-shaped	Straight lashes with no natural curve, and strong cat-eye looks
M	Similar to L, with a shorter flat base	Downward-growing lashes and very lifted designs

In the shop you’ll find speciality curls such as L, L+ and M among our lashes.

Diameters

Diameter is given in millimetres. Suppliers usually offer anything from 0.03 to 0.20 mm or more. Supplier guides broadly agree on the following:

Diameter	Typical use according to industry guides
0.03 mm	Mega volume (fans of many extensions)
0.05 mm	Full volume
0.07 mm	Light volume; also used in some classic or hybrid sets
0.10–0.12 mm	Classic, especially on fine natural lashes
0.15 mm (up to 0.18 mm in some sources)	Classic, only on thick, strong natural lashes
0.20 mm and above	Discouraged by some sources as too heavy

The key idea is that the total weight hanging from each natural lash must be proportionate to it. A fan of several 0.05 extensions can weigh about the same as, or less than, a single thick extension; Module 7 covers this in detail.

Lengths

Extensions come in lengths given in millimetres, either in single-length trays or mixed trays (for example, short mixed lengths for the inner corner and areas with short lashes). Remember from Module 1 that natural lashes rarely exceed 12 mm: the length you choose must respect the length and strength of each natural lash, and the full design is decided during mapping (Module 8).

Fibre types: mink, silk or synthetic?

The AAO EyeWiki describes extensions as synthetic fibres such as polyester. In practice the most common fibre is PBT (polybutylene terephthalate), a thermoplastic polyester that is shaped while hot and holds its curl as it cools.

The names “mink” and “silk” used by many brands usually refer to the finish (matte or glossy), flexibility or taper of the tip, not to what the fibre is made of. Several industry guides explain that “silk” extensions are not made from real silk and that real mink is practically never used in lash extensions. If in doubt, ask your supplier.

Adhesive: basic cyanoacrylate chemistry

What it is and how it sets

Lash extension adhesives are cyanoacrylate-based. An analysis by the Finnish Institute of Occupational Health (Lindström and colleagues, 2013) identified ethyl cyanoacrylate as the main component of the glues studied. Cyanoacrylates polymerise (turn from liquid to solid) by reacting with moisture: the thin film of water on almost every surface and the humidity in the air start the reaction.

Humidity speeds up curing and a lack of it slows it down. That’s why every manufacturer gives a humidity and temperature range.
Initial set is not full cure. The AAO EyeWiki notes that adhesive may take up to six hours to fully solidify, which is the reason behind aftercare advice for the first few hours (Module 9).

Humidity and temperature: what happens outside the range

Situation	Effect described by industry sources	What it means for your work
Humidity above the adhesive’s range	Curing too fast (“shock curing”); a whitish residue (“blooming”) and a weaker bond may appear	Poorer retention; use a slower adhesive or bring the humidity down
Humidity below the range	Slow curing; the extension can slide before it sets	Badly directed extensions; some data sheets note a weaker bond
High temperature	Curing speeds up	Less working time; the adhesive becomes runnier
Low temperature	Curing slows; the adhesive thickens	A more brittle bond, according to some sources

One industry source (LashBee Pro) puts the high-humidity threshold at around 70% for most adhesives, while noting it varies by product. Actual ranges differ widely between manufacturers: in Module 2 you saw two examples (18–22 °C and 50–65% for one; 15–85% humidity for another). So the rule never changes: measure with your hygrometer and choose an adhesive whose range matches your room, according to its technical data sheet.

Storage and daily use

Write the opening date on the bottle. Shelf life once opened varies a lot: for example, Lashbase states 3 months opened for its Advance adhesive, while London Lash recommends using Lady Bond ideally within 4 weeks (8 at most). Follow your product’s guidance.
Shake the bottle before use, as industry guides advise, and close it tightly after each use, wiping the nozzle.
Refresh the glue drop. A drop loses effectiveness over time; one manufacturer’s sheet gives around 60 minutes in optimal conditions and advises replacing it if it turns stringy.
Store it as the label says (temperature, bottle position, protection from light). If you keep it cold, let it reach room temperature before opening.

Adhesive safety

Safety data sheets for cyanoacrylate adhesives typically carry the EUH202 statement under the EU CLP Regulation, warning that the product bonds skin and eyes in seconds, along with classifications as a skin, eye and respiratory irritant.
The Amano study (Cornea, 2012) identified formaldehyde as the glue ingredient linked to the most eye damage in its case series, and an ophthalmologist at Bascom Palmer Eye Institute explains that these glues can emit formaldehyde. Buy from suppliers who provide both the technical and safety data sheets.

You’ll find professional adhesives and other liquids in our glue and liquids section.

Primer

Primer is applied to the natural lash before extensions. Manufacturers present it as removing oil and residue from the lash to help adhesion; some also credit their formula with balancing pH. Bear in mind that much of this information comes from brands that sell primers, and that the retention gains attributed to it are based mainly on professional experience rather than controlled studies. The same guides warn that too much product can lead to uneven curing or a weak bond.

Common guidance across the sources reviewed:

Primer does not replace cleansing: cleanse the lashes first, then prime.
Apply it with a lightly loaded micro brush, along the lashes and towards the base, without flooding the waterline.
Keep it off the skin and away from the eye; if it gets on the skin or pad, wipe it off before you start.
Let it dry completely before applying extensions (one guide suggests 30–60 seconds, or until the lashes are completely dry to the touch).

Always use it exactly as its manufacturer directs.

Removers

Remover dissolves the adhesive so extensions can come off without pulling out the natural lash. The main textures are:

Type	Characteristics described by manufacturers
Gel	Allows precise placement; usually described as the faster option and recommended mainly for experienced artists
Cream	Thicker and tends to stay where you put it; slower and easier to control, so it’s often recommended for beginners

Liquid removers also exist; being runnier, they are harder to control near the eye. Always follow the manufacturer’s processing time, and don’t use more product than you need. Safe removal technique is covered in Module 9.

A real-world warning about removers

In July 2025 Spain’s medicines and health products agency (AEMPS) ordered sales to stop and a recall of the Noa Nox Gel Remover because its composition could cause serious eye injury and, although it is a professional product, it is applied so close to the lash line that contact with the eye could not be ruled out. It’s worth checking cosmetic safety alerts from time to time.

Common mistakes

Choosing a curl by its letter without comparing the manufacturer’s chart.
Using diameters or lengths the natural lash can’t support.
Blaming the adhesive without having measured the room’s humidity.
Not writing the opening date on the glue and using it beyond the recommended period.

Module summary

Every extension is defined by curl, diameter and length; curls are not standardised between brands.
Fine diameters (0.03–0.07) are used for volume; 0.10–0.15 for classic, depending on the natural lash.
Most extensions are synthetic (usually PBT); “mink” and “silk” usually describe finishes.
Cyanoacrylate polymerises with moisture: outside the manufacturer’s range, retention suffers.
Initial set is quick, but full cure can take hours.
Primer goes on after cleansing and never on skin or eye; remover (gel or cream) is chosen and used according to the manufacturer.

Self-assessment

Why can’t you rely on the curl letter alone when you switch brands?

Because curls aren’t standardised: one manufacturer’s C can look like another’s CC. You need to compare the curl charts.

Roughly which diameter suits mega volume, and which suits a classic set on fine lashes?

Around 0.03 mm for mega volume; around 0.10–0.12 mm for classic on fine lashes.

What triggers cyanoacrylate polymerisation, and what does excessive humidity do?

Moisture in the air and on surfaces. If humidity is too high, the adhesive can cure all at once (“shock curing”), with possible whitish residue and poorer retention.

What does “mink” usually mean on a box of extensions?

It usually describes the finish or taper of a synthetic fibre (typically PBT), not real mink fur; if in doubt, ask the supplier.

Why doesn’t primer replace cleansing?

Because the guides treat it as a later step: cleansing removes make-up and dirt first, and primer is then applied to the clean lash, following the manufacturer’s instructions.

Sources

Note: this module is for education and information only and does not replace hands-on, in-person training with a qualified educator. Always follow each product manufacturer’s instructions: their technical data sheets take precedence over any indicative figure in this course.

Buy the course supplies

All the supplies for this course are available at Lash Canarias:

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