Kit is urethane 100% if you're lookin' for authentic if i'm not mistaken some do come in fiberglass. Their's many ways you can tell a difference between a real and a fake. If it's not black in color it's fiberglass. Some things to know fiberglass has different colors such as green, yellow, pink, blue, white. Most of the time urethane is black or dark dark gray. You can also knock on the bumper if you can't tell the fiberglass will tend to be hard and make a louder thump. Where as the urethane will be much softer and flexible and absorb the thumb such as your stock bumper.
If you can flex it pretty hard without breakin' it it's urethane
If you flex it and it cracks it's fiberglass.
One way to check and authenticate. Check the lines of accuracy also see if it has a certain serial, part #, certificate, tm, register, stamp, maker. You can compare with a picture of an original to what you plan on buying before you make a decision as well.
And if you plan on lookin' around just for any type of kit. Some other helpful checks if you buy a body kit most of the time you can never get a perfect kit you'll always need little bodywork to perfect errors ex: blemishes. But with the TRD
kit that's one perfect kit if it's authentic.
I'd recommend you to watch out for: Wheel arcs are they curved, crooked, off in anyway? Are the pieces fit to match close to perfect on the body? Are the holes to bolt up the kit pre-drilled or will you need to do the drilling? Any blemishes on the kit? Are some pieces to high/low/short/long? Does the kit you prefer have accessories such as specific grills, plugs, logos, badges. What color is the back of the kit? Does the kit have special documents & production make place? Are all the cut outs such as airscoops, mouths, vents, etc. for the kit properly shaped or warped? Other then that their are just some really really excellent fake kits. Some come urethane most fiberglass you can never tell though if you get a bodyshow to do great bodywork. Last ask if you can do a test fit it would usually help fitting it on the car prior to buying it it will make a huge difference. Just check it out and you'll be just fine.