The best replacement for synthetic is regular oil.

The best alternatives to synthetic are rated as following:
★★★★★  regular oil
★★★  conventional oil
★★  down sleeping bag
★★  natural vitamins
★★  synthetic blend
★★  conventional motor oil
★★  down
★★  analytic
★★  wood stock
★★  conventional
★  natural
★  natural makeup brushes
★  human hair
★  down sleeping bags
★  oil
★  analytic phonics
★  human hair wigs
★  regular motor oil
  mineral oil
  non synthetic oil
  analytic language
  human hair extensions
  hard coat stucco
  real diamonds
  mink eyelash extensions
  standard oil
  natural vitamin e
  conventional oil change
  cable winch
  blend oil
  high mileage oil
  organic fertilizers
  semi synthetic oil
  real hair extensions
  real hair wigs
  natural fertilizers
  artificial
  laminated rifle stocks
  natural rubber
  fully synthetic oil
  mink lash extensions
  leather saddle
  down bag
  natural thyroid
  leather cleats
  natural paint brushes
  real hair
  natural thyroid medication
  steel winch cable
  natural fibers
  petroleum
  bioidentical hormones
  regular engine oil
  leather soccer shoes
  real stucco
  reg oil
  wooden bowling lanes
  organic fertilizer

Your alternative for synthetic is not listed? Suggest!
Speaking about synthetic, one probably shouldn't forget about regular oil.

Other search terms related to synthetic and their ratings are:
★★★★★ regular oil
★★★ synthetic blend
★★ conventional oil
★ conventional
★ mineral oil
You have in mind a companion for synthetic and it is not yet here? Propose!



Google Trends

Scale is based on the average worldwide traffic of synthetic in all years. Click on graph for more.
synthetic
regular oil
conventional oil