Generally human.

Synthetic is very easy to care for, but easy to damage with heat, and it can reflect direct sunlight in a nylon-like manner. Synthetic can also develop a damaged texture after a few months due to night time pillow abrasion. But if you are in the sun all day, or in chlorinated swimming pools, synthetic may be better for you because the original color is permanent.

Our synthetic is Kanelalon and it's rather nice. We cannot bleach the knots though!

Another instance where synthetic may be better is for tight curly hair, or for platinum blond or gray hair. When human hair is permed tight or bleached light, the quality suffers a great deal, to the extent that synthetic hair feels nicer than human.

Synthetic hair makes the best gray. Human gray can appear yellow either immediately or over a period of time, because the donor was probably young with dark hair. Natural gray donor hair has become virtually inpossible to obtain. Yak hair is very bright white and shiny and is not strong, so it can break and shed. For an all-grey or high percentage gray unit we can mix a blend of all three gray types upon request, but all synthetic looks very good.

Exception: Ultra violet light (blacklight). If you frequent night clubs, halloween parties etc where UV is the only light, then synthetic gray hair will glow brightly. So if your hairpiece is on the top and your real hair is at the back and sides, you will see where the hairpiece ends and the real hair below will appear dark by comparison.