Eyelash extensions come in all sorts of lengths, widths, curls and materials. The curl is usually a matter of preference for the customer. The length is generally dictated by the length of the customer’s natural lashes. What about width?
Leaving volume lashes out of it, because they use ultrafine extensions applied in groups, the most thicknesses you’ll find available for single artificial lashes are: 0.10 mm up to 0.25 mm. Just about everyone agrees that 0.25 mm lashes are going to be too heavy for most customers. At the other end of the spectrum, there is general agreement that 0.12 mm lashes are only suitable for customers with thin or weak natural lashes, which can’t sustain anything thicker and heavier.
So, we are then left with 0.15 mm, 0.18 mm, and 0.20 mm. Some therapists swear by 0.20 mm. They say this width is ideal for natural lashes, and that they are the most popular width, which suits most people. Others say that 0.20 mm lashes are suitable only for clients with especially strong natural lashes, and for that reason they only use them very rarely.
It seems likely that initially 0.20 mm lashes are popular with clients because they want nice thick eyelashes. But if these lashes are too heavy for their natural lashes, they are going to fall out faster than they should do. So perhaps when these customers come back a second or third time, they may be more realistic about the size of lash their own lashes can carry, and adjust their enthusiasm for 0.20 mm. Perhaps it is on the return visits for further eyelash extensions that 0.15 mm and 0.18 mm extensions become the most popular. It would seem that these are the most likely widths to work best with most normal, healthy eyelashes.
You would naturally go for thinner ones for people with very fine natural eyelashes; and it will only be the customers with thicker natural eyelashes which can physically sustain 0.20 mm eyelash extensions, who will continue to choose that width.