Plastic is a synthetic material that can made into almost any shape. Plastic is commonly found in water bottles and bags that tend to be very flimsy. However, when you add a glass fiber reinforcement this already great material becomes stronger than some metals. The strength-to weight ratio of Fiberglass Reinforced Plastic compared to metal or wood products can be up to 5 times bigger. The fiberglass strength is maintained due to the fact that the fibers carry the load while the resin distributes the weight throughout the composite parts as required.

Will a car break it?

This manhole lid was put through the test. First, we made sure it held a person; ..easy! We decided to take it to the next level by driving over it with a car. The car’s weight pushes the fiberglass manhole cover down. However, right after the car rolls off the other side, the fiberglass manhole lid pops right back into place. Making large customized shapes and pieces out of fiberglass is much easier to do than with most other materials. Additionally, this piece weighs very little for its size and can be moved by one person. If this same piece were to be made out of metal, it would be very difficult to move.

Car - Fiberglass Strength

Diesel Truck?

Next, we cut a piece out of the fiberglass manhole barrel and we had a large truck run over it. As you can see, it doesn’t completely flatten it to the ground but it does flex slightly. Once the truck rolls off the fiberglass piece, it goes right back to its original form. If wood bends, it will snap and will be structurally unsound from there on out.


Ok let’s just jump to the extreme (and most exciting!) one; a fully loaded semi-truck! As you will see the fiberglass still does flex, and once the wheel of the semi rolls off the piece of manhole, it still retains its form. If you had a sheet of metal that bent in the same matter, it would not retain its form after the force. This can be a huge issue if you need your material to keep its shape and withstand tough forces.

Which will break from a sledge hammer: steel, wood, or fiberglass?

  • Piece of steel easily dents and loses its shape.
  • Piece of wood snaps in half (of course) and becomes structurally unsound.
  • Piece of fiberglass has a few cosmetic scratches, but keeps its form AND strength.
Sledge HHammer - Fiberglass Strength