How do you unwrap an object like clothes so that it’s UV turns out like an even square grid?
It’s a bit annoying when I’m trying to unwrap something like this.
But it turns out like this:
Here’s the skirt mesh I used for my example:
You need to seam it. In the case of this mesh, assuming it’s a “thin” mesh, just select a series of edges from the top margin to the bottom margin and mark as seam (ctrl e menu for me), then unwrap it.
Well, that SEAMS to help, but I’d like all the faces to have the same surface area when they’re unwrapped, kind of like the first picture I posted. I put seams on the top, bottom, and the back.
Get the TexTools addon. Command is Rectify
You can also do it natively in blender, but requires more steps, and would take me longer to explain.
Check out this vid on UV unwrapping techniques in blender
The correct method to get dresses is by shaping them into several pieces and cut and sew them as a tailor would do; this way, if you unwrap them before simulating you’ll also get perfect UV maps.
Okay, but is there a way I can UV unwrap them to look like this after they’ve been shaped? Not even necessarily simulated?
Looks like an awesome addon! Just… how do I install it? 
a simple youtube search:
Cool! One more thing, will this addon (textools) work with version 2.79?
Yes, you can if the mesh is suitable, for instance with the addon that @OrAngE has posted above , but I can’t get why you should do that, if you model a flat shape and unwrap it then you obtain the best UV map for texturing the fabric, it doesn’t have to be a squared grid, it must resemble the shape of the piece of cloth.
No. That link was for 2.80.
But if you follow the link you can see that there is a 2.79 as well, which will work with 2.79.
http://renderhjs.net/textools/blender/
Do yourself a service, you should jump off the 2.79 train, and catch the first 2.81 zooming by!
If all is quad, I use:
- Select some random face and UV Reset.
- Select all, then UV Follow Active Quad (with previous quad still being the active quad - don’t deselect).
- In UV Editor, select all, activate constrain to image bounds and scale about 2D cursor to fill space.