Mine is mostly not covered. The only cover I use is the length it takes to get to my hand in my normal helm position. That way I have a little softer handle for sheeting.
The core is the strength of the line and it is treated so that it can be used openly in the sun. Stripped, it really runs through the blocks easily.
Of course, I am also using the 8:1 Ratchamatic which is awesome.
Rick