Flat lashes are flat at the base and taper off at the end to give a wider look. They look absolutely stunning in classic sets thanks to their rich black matte finish. They give more volume than the traditional classic eyelashes since their base is wider and larger than the traditional ones.
Flat lashes can also give better retention than a regular classic set. As you probably know as a lash artist, the base is one of the things that can cause retention issues when getting eyelash extensions. If the base is properly attached to the natural lash, it will give you better retention. Flat lashes have wider bases, which allows the natural lash and the lash extension to bond better together.