What is inside of a highlighter? Highlighter or ink?

Question

My roommate swears it's highligher. I'm pretty sure it's ink and he's an idiot. What do you think? Ink or highlighter?

Answer 1

Peanut butter of course!

Answer 2

That's a good question, HIGHLIGHTER is a brand name.
There are several brands of felt-tip marking pens but they are all mostly the same in respect to the basics.
The felt tip is a semi-hard porous plastic material (genuine felt is a cloth-type material) with a 'feed' on the bottom that sticks into a cylindrical foam-filled tube that holds the fluid colorant.
When you hold a felt-tip marker to use it the fluid settles to the bottom, which is the application tip.
Gravity and fluid absorption causes to ink to go to the tip.
As the ink gets used up there is less ink to fill the application tip and the original line that had been made the width of the application tip becomes 'splotchy' (irregular).
So, the answer is that most of what's inside a highlighter is different kinds of plastic.
Probably at its newest, fullest capacity, the ink comprises from maybe 25% to at the most 50% of the 'guts' of a highlighter.