The best replacement for polyurethane is varnish.

The best alternatives to polyurethane are rated as following:
★★★★★  varnish
★★★★  lacquer
★★★  urethane
★★  silicone
★★  polyacrylic
★★  epoxy
★★  polycrylic
★★  rubber
★  shellac
★  latex condoms
★  pvc
★  polystyrene
★  rubber bushings
★  tung oil
★  fiberglass
★  stain
★  wax
  wax finish
  paste wax
  oil based
  polyester
  latex mattress
  neoprene
  oil
  enamel
  eva midsole
  oil finish
  spar urethane
  rubber air hose
  urethane finish
  mudjacking
  polyisoprene condoms
  lacquer finish
  polyethylene
  oil based polyurethane
  polystyrene insulation
  nitrocellulose
  polyethylene foam
  isocyanurate
  neoprene rubber
  acrylic
  wood molding
  alkyd
  polyurea
  polyisocyanurate

Your alternative for polyurethane is not listed? Suggest!
Speaking about polyurethane, one probably shouldn't forget about stain.

Other search terms related to polyurethane and their ratings are:
★★★★★ stain
★★ streaks
★★ foam brush
★ mineral spirits
★ chalk paint
★ isocyanate
★ fiberglass
finish
stain in it
You have in mind a companion for polyurethane and it is not yet here? Propose!



Google Trends

Scale is based on the average worldwide traffic of polyurethane in all years. Click on graph for more.
polyurethane
varnish
lacquer