You can use cotton or poly. Rayon to soft I think.
Cotton is gorgeous and poly is ok too. The important
thing is to use same thread in the bobbin as the top.
If using cotton clean thoroughly in bobbin and anywhere you see fluff after ea. angel.

I have a lot of the Tavernmaker FSL designs and they recommend using good ole serger thread on both top and bobbin...I know sounds crazy, but it works! Strong, durable and looks like cotton, no sheen like using an embroidery thread. I made several of their bags using this thread...just beautiful!

I use rayon because it makes them shiny, and I like shiny. Never had a problem doing FSL with rayon. I think all the types of thread will work, depends on how you want your angels to look as a finished product. I like the idea of using serger thread---never tried that, and I've got scads of it around----

WELL MY DEAR I HAVE USED FROM THE MOST COSTLY TO THE DOLLAR STORE WHITE AND I LIKE THE CHEEP ONES BEST EXCEPT WHEN I NEED A SHINE I USE RAYON LOL A LOT OF HELP I AM RIGHT LOL HUGS CAROLYN

I do believe it depends on the look that you are trying to acheive. I generally use embroidery thread in the top and bobbin - however if I am trying to get an antique look (old-world) I will use serger thread in both the top and bobbin - it cam be messey - because the cotton tends to shed some - so you have to clean the bobbin area and watch for fuzzies on your needle area.

Overlock thread is the most economical,also you can use Bobbinthread in the Bobbin if using white color.Use a 80 metalic Needel und doublelayer of Stabiliser with a Layer of Scraps inbetween und that will let you stich the most dence Designs.Ursula

I love FSL made of rayon, they are strong and shiny. I use Vilene as WWS and same thread top and in the bobbin. The only time I don't use rayon is when the design is crochet-like or Battenberg lace and are not dense, in these cases I use embroidery cotton No.50 which is thicker. If you use cotton, remember to clean the bobbin area very often.

I love my cotton thread! I use badgemaster, I heard it helps piece shrinks less and tepid water to soak! I use metallics and rayon for edging and interest.

thanks for the tips ladies!!!!!!

Thanks for asking this question and thanks to everyone who responded.
I'm going to try serger thread.
AlmaG.

Thanks for asking! I want to do fsl but I'm kind of afraid to! One day I will just dig in and do it!

Thank you, I also wondered and am thrilled with the responses as I have enough of the suggested threads to try a project. Next on my to do list.

Just dive in and give it a go. I've made FSL designs with serger thread, polyester, rayon, and anything else I can find. Everything has a different look. Enjoy the process. I made a luminary last night with poly thread. It turned out beautiful. Even hubby was admiring it. So give yourself permission to experiment. You will be amazed at what happens.

Thanks to all you ladies, I never heard about the serger thread. I think I will try them all and keep samples for the future designs. Thanks again,Midge