Basics

Also reffered to as Latex, or simply Rubber
Polymers produced by plants (Mainly Isoprene)
Often extracted from the Rubber Tree and ocassionally Dandelions
Used mainly due to lower cost than Synthetic Rubbers or Elastomers
Also in some applications such as tires (especially for the landing gears of aircraft) the high heat resistance is of use

OSE Sources

Rubber Trees are Difficult to Grow outside of the proper zones
Most likely dandelions will be used
Latex comes from Osage Orange's fruit too, and there are tons of them out there on FeF