What are the lines on panel for?

[Jon Acton]

I love to ask this question.
Believe it or not there is a reason for the lines.
Does anybody know?
I'll answer next time.
Jon Acton

[David Oxhandler]

I thought they put 'em there so I would know which way was up when I hang the panels

[Mark]

To make it look like T&G boards, ie individual boards making up the wall.
T&G ceilings (and even roofs) use to be very popular.