FRP rebar is comprised of two elements; a fiber (usually carbon, glass, aramid, or basalt) and a matrix resin (polyester, epoxy, or vinyl ester). The role of the matrix resin is to hold together, protect, and transfer the load between the fibers.
First, FRP is much lighter than steel, up to 7 times to be exact!
The second is that FRP rebar is much less stiff, or technically speaking, FRP has a modulus of elasticity that is 5 times less than that of steel. To learn about how the lower modulus of elasticity can be beneficial in slab on grade applications.
But the difference goes further than that:
FRP rebar is corrosion resistant, where steel will eventually rust and crack the concrete it’s supposed to reinforce. This leads to structural life that is up to 2 times longer when FRP rebar is used!
FRP has a greater tensile strength than steel
FRP rebar is thermally and electrically non-conductive