The technique I am about to describe allows you to underline a garment and finish the seams in one procedure -- this makes the most beautiful seam finish and is not much more work than simply underlining (less, if you are planning to hand baste the layers together). This works on almost any vertical seam such as the side and center back seams of a skirt (or the seams on a gored skirt) as well as princess lines. I cannot take credit for this idea. The first place I learned about it was in a class with Cynthia Guffey but I believe the technique has been around for many years.
When cutting your underlining, add 5/8 inch to the seam allowances along the vertical seams. If you are using 5/8 inch seam allowances you'll cut them 1.25 inches wide. Place the underlining and fashion fabric RST and pin the vertical edges together -- the underlining will not lie flat as it is bigger than the fashion fabric. Sew these edges together with a 1/4 inch seam. Turn the panels right sides out. Press the edges so the underlining wraps around the edge of the fashion fabric and lies flat -- this looks a bit like a Hong Kong Finish. The following photo shows what this will look like.
The piece on the right is what the fabric piece will look like once the pressing is complete. The piece on the left is what the seam will look like once it is sewn and pressed open.
Once this part is completed you treat the two layers as one and complete your garment as usual. You can baste the upper edge together if necessary.
Here's a picture of the inside of a wool skirt where I used this technique, underlining with silk organza
This is a picture of a skirt made from sheer pink linen.
On this skirt I had planned to line but not underline. I discovered that the linen fabric was so sheer that the pressed seam allowances showed through unattractively. I used the lining fabric (bemberg rayon) to underline and finish the seams which also prevented any show-through of the seam allowances, a benefit lining would not have afforded.
This is an easy and elegant way to finish any vertical seam in a garment. It eliminates the need for a lining and gives a couture look to the inside of your garment. I don't think you will be disappointed in the results.
I get lots of questions about the best way to add the 5/8" seam allowance to the underlining fabric. Here is the method I use.
After I cut out my fashion fabric I place the pattern on the underlining fabric. I attach a Removable Rotary Guide Arm (made by Olfa) to my rotary cutter and set the distance from the blade to 5/8".
It is then a simple task to guide the arm along the edge of the pattern while the blade cuts 5/8" away from the edge.