The number stands for the amount of extensions applied to each natural lash. 3D is three extensions adhered to one natural lash, and 5D is five extensions adhered to one natural lash. So, you are literally getting 3X to 5X more lashes with each and every full set and touch up!If you want real mink lash with better three-dimensional effect and richer gross, then choose 5D mink lash instead of 3D mink lash. But there is no big difference between 3D lash and 5D lash. Choosing good eyelash quality, beautiful eyelash style and suitable price is more meaningful than 3D or 5D.