The unwrap factor is a sliding scale from 1 character to the end of the line. The factor determines how long a line has to be to be added into the paragraph with the lines above it.
This is a full line of text.
This is a full line of text
that should not end.
An unwrap factor of 0.5 (the default if 0 is set) will add any line longer than half the page to the line above it. The first example will not be unwrapped while the second one will.