They say that the J-Curl got its name because it looks like a ‘j’. I can see it, sort of. It would have been much more helpful if the inventors of these curls had stuck to a sensible progressive A .. B .. C .. list, rather than naming them after letters they vaguely resemble.
The J-Curl lash is the straightest of the extension lash types. But it is not completely straight. It is slightly curved, with an additional ‘flick’ at the tip.
Since J-Curl eyelashes have an almost straight shaft, they will bond very well with natural lashes which are straight or have only a slight curl. That is the case with the average natural European lash. But J-Curl lashes won’t bond well with naturally curly lashes because of the lack of a large shared surface area.
For anyone who has with hooded eyes, J-Curl lashes may be the best choice. You wouldn’t be able to use a strong curl with such eyes, because the lashes would be likely to scrape the eyelid. (Another possible option in such circumstances is an L-Curl, since it starts straight and then has a strong curl only towards the end.)
The J-Curl is also often suitable for people with protruding eye shapes, because it avoids attracting attention to the prominence of the eyes.