How to tell if material is natural or not

I buy a lot of my material for smaller projects from thrift stores, I never really learned how to tell quality or near quality material like linen, cotton, etc. from other materials similarly looking or feeling.  Most of the time these pieces of material have no tags, so I have to go by what I think.  I veer away from stretchy anything as I hate that material. I know the obvious materials, but some of these blends I am a bit confused with.  I prefer higher % linen, cotton, etc. But finding it 2nd hand is hard and good material is expensive to buy out right, even on sales.

Any thoughts & suggestions are welcome!!  Thanks --Tess

Have you seen this permies thread? https://permies.com/t/274034/natural-fibers

Unfortunately, you can't do a burn test on fabric you don't own, but once you've taken an outfit home, checking it out may help you know more for the next time?

Jay Angler wrote:Have you seen this permies thread? https://permies.com/t/274034/natural-fibers

Unfortunately, you can't do a burn test on fabric you don't own, but once you've taken an outfit home, checking it out may help you know more for the next time?

Thank you Jay!  I will check it out  --Tess

You might be able to tell by how wrinkled the fabric is.

A synthetic blend might be softer feeling and less wrinkled.

Jay Angler wrote:
Unfortunately, you can't do a burn test on fabric you don't own, but once you've taken an outfit home, checking it out may help you know more for the next time?

Sometimes the way the fabric is cut or the way the seams are, you can tease out a loose thread, take them outside of the store and pull out your trusty lighter to see what happens. (yes I'm that wacko outside the salvation army trying to find good light as I set things on fire. actually let's be honest, the vast majority of the time I buy the thing first and rue my decisions later, but every once in a while the voice of reason wins out.)