First, It's Not Knit, It's Grenadine
Even if you haven't heard of a grenadine tie before, you've likely seen one—and possibly mistaken it for a knit tie. It's a common mistake.
The grenadine tie and the knit tie are more like distant cousins. While the knit tie is formed through (you guessed it) knitting, grenadine is a woven fabric produced by a loom.
Grenadine ties superficially resemble knit ties because of the particular method of weaving involved: The weft and warp are twisted around each other in such a way to produce a highly textured fabric with much visual interest.
However, knit ties are best worn in slightly more informal settings, as they lend a casual air to an outfit. Meanwhile, grenadine ties can be appropriate for both semi-formal and formal wear.