Material
The extensions can either be made of natural fibers or synthetic material.
Synthetic lashes are the most common type by far. They are made of polybutylene terephthalate (PBT), a type of polyester.
Natural fibers range from mink, silk, sable and fox. They are rarely used in lash salons because of their many disadvantages (I discuss them in this article).
Length
Lash extensions come in a variety of lengths, ranging from 6mm to around 18mm.
The most popular lengths are between 9mm to 13mm, which is very close to the average lengths of natural lashes. This help to create a natural look that blends well.
Curl
There are many, many, many curls to choose from depending on the curl of your own natural lashes.
You can typically find extensions with I, J, B, C, CC, D, CC, DD, U, L, and M curls.
Out of them, the C and CC curls are the most popular ones. They add just a slight lift to the lash, without making it look too dramatic or curled.
Diameter
The diameter refers to the thickness of the extension and is calculated in millimeters.
It typically ranges from 0.03mm up to 0.25mm or more.
We usually use the thinner extensions for volume when we want to create a volume fan (0.03mm and 0.05mm) while thicker diameters would be reserved for classic lashes.
Color
Black is the most common color by far, but there are also options to choose from such as brown, ombre, blonde and even colored lashes.
You can play with hues of red, pink, green, blue, orange, purple, white and gold to create unique looks for a very special occasion.