How could I make something like this:
in Illustrator/Sketch? I've seen similar questions here but this style looks different enough: it almost likes like 3D with "shades".
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You can envelope distort with a mesh a bunch of uniformly spaced parallel lines:
This can go astray if you drag some node past another because the space between the lines is transparent. The result will be easily a mess (see NOTE1). If you have a bunch of adjacent filled rectangles instead you'll do not have that problem:
Before envelope distortion the rectangle pattern was this:
Envelope distortion can make regular looking bends if you move several nodes at the same time:
But quite complex foldings can also be manageable:
If you want recognizable well drawn 3D forms, for ex. Text or something else which must be geometically exact you are in a trouble. Complex forms are possible but the needed amount of patiency is colossal. Stretching a bunch of straight lines isn't optimal, it can be better to draw the needed curves one by one. Working with a 3D program is much easier if the forms are simple enough.
Script programmers can make Illustrator draw 3D-like curve patterns automatically if they can cope with the math. One example:
This is a screenshot from author's webpage:
NOTE1: It's not a mess in the hands of a person who knows what he does. It can be used as an artistic effect - a kind of folded gossamer.
These are very nicely crafted "Blends" created in Illustrator.
Draw several lines and select them. Go to Object> Blend> Make. Then go to Object> Blend> Blend Options and switch from Smooth Color to Specified Steps. Play around with the number of steps. While the blend is still "Live" you can adjust the anchor points on your original lines with either the direct selection tool or the anchor point tool.
The rest is artistry on the part of the creator of your examples.