I am hoping to help with identifying fabric for those who have some difficulties in that area.  Both fiber content, and weave seem to give a lot of sellers and buyers problems. 

First of all, let's start with weave.  Satin is a weave, not a fiber.  Some people think of satin as a kind of fabric like silk.  Not so.  Silk is a fiber.  One is what a fabric is made from, while the other is the finished surface of the fabric.  Satin has a very smooth finish, with a gloss to the surface.  Some satins are high gloss (very shiny), while other satins are low gloss.  Satin can be made of cotton, wool, polyester, acetate, silk or other fiber.  It just depends. But they are all very smooth and silky to the touch. 

   Hi-Gloss Satin  Dull Satin

 

Taffeta is also a weave.  Taffeta has been traditionally used for evening gowns and formal wear, and has an almost ribbed look to the weave (you have to look closely - it is a small, close weave), and it is stiff and makes an unmistakable rustle-ly sound as you move in the dress.  It was prized as much for the sound as for the fact that it is a strong, sturdy fabric.  It sometimes has a shiny finish, but not a smooth shiny surface like satin.  Taffeta is quite often cross-woven with different colors, creating an iridescent effect.  With one color on the woof, and another on the warp, the fabric will often look one color from one direction, and a different direction will give you a new color or shade.  The next pictures are of iridescent silk taffetas.  Taffeta can be made of just about any fiber, although polyester, acetate and silk are the most common.

   Yes, I know, a vile color, but this cross woven silk demonstrates admirably how the process works with the different colors on the woof and the warp.  As the viewers aspect changes, so does the perceived color of the fabric.   The lavender iridescent taffeta here:     is more subtle, but also a cross woven fabric.

 

Now we can touch on fiber.  How do we differentiate between cotton and polyester fabric or between silk and synthetic?  We can guess, but then we risk mis-representing the item to our buyers.  I have seen a lot of 'silk' items that were no such thing.  It looked silky, therefore the seller thought, 'good enough'.  No, it isn't.  Make sure!!  It only takes a moment, and it's easy.  Here's how.

You will need the following:

Tweezers;  matches or lighter;  small sliver of the fabric (about 1/4" X 3/4") triangular shaped

Take a small sliver of the fabric in question.  If it is a garment with no tags, look for an inside seam or hem where a small sliver won't be missed.  Go to a well ventilated area, but one with no breezes or drafts.  Holding the sliver of fabric in the tweezers, apply flame to the narrow end of the fabric and observe the results CAREFULLY.  If the fabric burns, it is natural fiber.  Either cotton, linen, wool (toxic!!), rayon (yes, rayon is a natural fiber.  More about that below.), flax, ramie or other.  If the fabric melts, it is synthetic.  Polyester, nylon, etc.  If it both burns and melts, it is a blend.  Now, you might have noticed I haven't mentioned silk.  Silk reacts in a unique way to flame.  It goes almost immediately straight to ash.  It burns so rapidly, you really do not see the burning - basically, you apply flame, you see ash appear.  Neat, really.  But remember, it is not much more than a kind of spider-webbing, is it?  So if you keep that in mind, it isn't so shocking that it goes up so fast.

Now, Rayon.  I know you were probably gob-smacked to see me say that Rayon is a natural fiber.  It is.  It is man made, but of natural materials.  It is for all intents and purposes the same as paper.  It is made of wood.  Made differently than paper, it is pulled and spun, but made from wood.  That is why it doesn't wear all that well (wrinkles, tears easily, no bleach, wears out quickly), but is soft, comfortable, absorbent and breathes well.  It was also the very first man-made fiber.  First made in the late 1870s, I believe?  I might have the decade wrong, but the century is right.  Amazing, huh?   Good stuff, but treat it gently.

NEW! Acetate.  I have just found out that acetate is also a natural fiber.  Yep!  It is kith and kin to rayon, developed in 1924.  Also made from wood fibers.  Extremely delicate, more so than rayon.  However, just shows to go you (old family twist tongue), that you learn something new every day!

Last word on silk before I go;  NEVER, ever with the bleach!  It will yellow your silk, and cause it to weaken and tear.  Also, heat is a silk killer!!  If at all possible, hang dry your silk, or fluff dry.  YES, silk is washable!  Everything is washable!  All you have to do is wash the fabric BEFORE you cut and sew to make the outfit washable.  That doesn't mean you want to wash everything - lined blazers never look right after washing!  Trust me.  But even wool is washable, if you start it that way.  How you start is how you continue.   If you haven't washed your silk, rayon or wool - better count on dry cleaning that outfit after you make it!!  It will never hang right.  Guaranteed.