The best replacement for cardboard is plastic tampons.

The best alternatives to cardboard are rated as following:
★★★★★  plastic tampons
★★  corrugated
★★  styrofoam
★★  plastic applicator
★★  paperboard
★  cardboard
★  plastic milk cartons
★  carton
★  corrugated paper
★  card stock
  plastic applicators
  fiberboard
  plastic boxes
  cardstock
  landscape fabric
  non corrugated
  chipboard
  paper recycling
  fibreboard
  card board
  plastic storage

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

Other search terms related to cardboard and their ratings are:
★★★★★ fiberglass
You have in mind a companion for cardboard and it is not yet here? Propose!



Google Trends

Scale is based on the average worldwide traffic of cardboard in all years. Click on graph for more.
cardboard
plastic tampons
corrugated