via The Beauty Brains

Havoctheory says…I heard that conditioners contain ingredients such as polymers with reflective qualities to coat hair strands. They reflect light and therefore makes your hair shiny. Is
this true? What kind of chemicals would also produce this effect?

The Left Brain responds: 

This question comes from our Forum where Pufff added this comment:
“Hey! I actually was just thinking about this the other day! I was
reading the ingredients on some of the old gel I have and saw it used a
polymer which surprised me cause isn’t that plastic??? The gel did make
my hair look shiny soooo who knows.”

Polymer does not equal “plastic”

It’s true that polymers are used to make plastic. But that doesn’t
mean that every polymer IS plastic. A polymer is simply any chemical
compound made up by a number of small repeating units which are called
monomers. Depending on the type of monomer (or monomers) chosen,
 polymers with different properties can be created.  For example, when
propylene monomers are strung together in a long chain the result is
polypropylene, a common plastic used to make a variety of packaging
materials.  On the other hand when acrylamide and
diallyldimethylammonium chloride monomers are combined the result is
Polyquaternium-7,  a common air-conditioning agent. These materials are
both polymers but they have very different physiochemical properties.

How do conditioners make hair shiny?

You have the right idea when you say that polymer ingredients reflect light to make hair shiny. Actually what happens is the ingredients smooth the cuticle of the hair. (Remember the cuticle is made of tiny shingle-like structures like the ones you find on your roof.) When these “shingles” become loose and start to stick up they cause light to reflect unevenly from your hair. This uneven reflection makes your hair look dull. Smoothing the cuticles allows light to reflect evenly which makes it look shiny.

Which ingredients increase shine?

The shine increasing ingredients are the ones that do the best job of
smoothing the cuticle.  Here are few types of ingredients to look for:

These are are excellent conditioners even though they receive a lot of bad press. Dimethicone is one of the best for smoothing the cuticle. Look for ingredients that end in “-cone” or check this list of Silicone Ingredients Used In Hair Care Products for more details.

Fatty conditioners
These “quats,” like stearalkonium chloride, are good at lubricating
hair as well. Look for ingredients that end in “-ium chloride.”

Mineral oil, meadow foam seed oil, avocado oil, coconut oil, are good shine enhancers. These work best from leave in products because the oils are not chemically modified to stay on your hair after

*What enhances your shine?!*
CN Says:
For me, Henna’s the ultimate shine enhancer. Again, because it helps the cuticle lay flatter and adds to the ‘baby doll hair effect’… with more substantial, smoother strands that reflect light a bit better.  Also, many of my favorite conditioners including Redken’s Butter Treat including cheapy drug store conditioners like Aussie Moist and Herbal Essence’s Hello Hyrdration, when left in, leave me shining… but only when I’m lighthanded.  Use too much and my hair is ashy and dull.
Finally, that Aveda Anti-Humectant!  It leaves a shine on my hair like none other… I may revisit with my upcoming trip to humid ass Charlotte!