I'm not really a clothing design expert, so I made this suit by attaching laser cut faux leather to a store-bought undergarment instead of sewing *everything* from scratch.
Your undergarment needs to have the following characteristics in order to work for this project:
You want an undergarment that is pretty much form fitting (I got one that was a size too small for me on purpose).
You want something that can diffuse light well, and absorb very little light.
It is recommended to use something with flat seams on both sides of the garment. This will make your life *much* easier when it comes to attachment of the light blocking material.
This requirements pretty much limit your search to lightweight athletic performance base layers. For the record, I ended up using an REI Lightweight Polartech Power Dry Base Layer
as my undergarment.
For the overlay material, you need something that is going to be completely opaque to very bright LEDs, yet laserable. This limits your choices pretty much right off the bat to some sort of synthetic leather (which stinks since it is still kind of spendy...I'd love to hear of other lightproof, wearable, black fabrics that people know of in the comments below). I used some Home Decor Fabric made from polyurethane