What is Emulsion Ink? The definition of Emulsion is The suspension of liquid in a liquid. As of today this is the 4th generation ink formulated by Zebra Pen. Though Hybrid inks have been introduced to the writing instrument market none of the formulations have porduced the full emulsion ink properties now offered by Zebra Pen. Smoothness is defined by the Coefficient of Friction: The ratio between the force necessary to move one surface horizontally over another and the pressure between the two surfaces. The Z-Mulsion has the lowest (best) friction measurement of anything currently on the market. Emulsion Ink Retractable Pen is consumer approed sophisticated barrel. Absorbent rubber grip for a comfortable write. Super smooth ink glide. Sturdy metal clip. Refillable with Zebra EQ-Refill. Medium 1.0mm point size. Assorted colors inlcude: Black Blue Red Light Blue Violet Green Pink and Orange.