The easiest way to identify the content of your fabric is a burn test.  Burn tests follow a couple of simple rules.

1. Do it in a ventilated area.
2. Have water handy.
3. Have a lighter, not matches, the long one’s used to start fires or light candles work   better.
4. Have a non-burnable work surface.  Porcelain or metal camping plate works best.
5. Have a set of long handled tweezers or in a pinch metal salad tongs.

How fast a fabric burns, what color the flame is, type of smoke and color and of course smell, will all tell you almost exactly what type of fabric you have.  Natural fibers smell like burning paper and have a pretty white and full smoke.  Synthetics are a darker smoke and sometimes black depending on the fiber content.  Polyester tends to burn for about a 3 to 5 count.  One-one thousand, two-one thousand, three-one thousand…etc. and then go out.  Acrylic (yuck!) will keep burning till it is s bubbly, putrid, sticky, charred, mess all over.  Is why it is not used in the scenery and display industry.  Too hazardous.  Polyester is inherently fire retardant though, which is weird considering it’s base make-up.  There are tons of charts online that will give you smell, smoke color and thickness, and ash results that will tell you what your fabric is made of and you only need to use a small strip or even thread or two to figure out your fabric content.  Here’s couple sites to reference. http://quilting.about.com/od/fabricembellishment/a/burn_test.htm, http://www.lindrix.com/fabcontent.html, http://www.fiber-images.com/Free_Things/Reference_Charts/free_reference_charts_fiber_content_guide.html.

This is a great experiment for kids as long as they are monitored.  It’s science at it’s easiest.  There are chemical tests too,  bleach does interesting things to wool and rubber.  Have fun!