But in my experience the best product is a vinyl flat trim that matches the window frame.
How to install trim corners around windows for vinyl siding.
Instruction on how to install exterior 2x4 trim around a new or old window.
When installing window molding start at the top.
Install the tops first then the sides and then the bottoms of the window surrounds.
After the insulation is in place you want to install trim around the inside to finish the job.
Along the tops install j channel trim with horizontal siding and base trim with vertical siding.
Cut the trim so it is two channel widths longer than the opening s width.
Install j channels at doors and windows and under roof eaves and rakes.
Here s how they do it.
It s all done by eye with a sharp pencil a miter saw and an 18 gauge nailer.
Most trim carpenters don t even use a tape to trim windows.