As you are adding multiple lashes to each single natural lash you have to have an extremely fine and lightweight lash so you will need to use either 0.05, 0.06 or 0.07 weight lashes. 0.07 is the most commonly used lash for this technique. You can add up to 6 of the lashes to the natural lash but obviously this will depend on the strength of the natural lash. You don't want to weigh them down too much.
As the name suggests, this technique focuses more on adding density and volume rather than length and you only really want to go about 2mm longer than the natural lash. You will find by keeping the lengths shorter that you will achieve a fuller effect.
(As a side note though, I do have clients that like to add a bit more length using volume lashes so if they want longer I adjust the number of lashes. So instead of maybe having a 5 or 6D effect I would go longer but only do a 3D effect. My most popular set is a 50/50 mixture of volume and Classic lashes. Clients like that their lashes look fuller but it's not quite as pricey as a full volume set).
Originating in Russia, volume lashes are a new advanced technique that give client's safe yet stunning volume. With classic lash extensions you are limited by the number of natural lashes your client's have as only one sythentic lash is bonded to your natural lash. This is great if they have a lot of strong, natural lashes to work with, classic lashes will create fullness and add length. However, if their lashes are quite sparse and fine there is a limit to what length and thickness can be safely attached to their lashes.
Volume lashing goes beyond the conventional one-on-one eyelash extensions by using incredibly soft, light and fine lashes. As these lashes are so much finer, volumization can be achieved by adding multiple extensions to create depth. With up to 6 lashes per natural lash and a variety of curls you can create a beautifully full yet natural look up to an incredibly glamorous set.
Volume lashing takes a great deal of practice and dedication but you can create some beautiful sets once you get the hang of it. Just don't give up or rush it. Your movements have to be very precise and you need to have the best products and tools available. I have spent a fortune trying to find the best tweezers for the job but believe me it will make such a difference to your work if you have the right ones! Practicing picking up volume fans with tweezers that aren't perfect will drive you insane and leave you cursing like a sailor!