Material Properties of Glass Fiber composite (GFRP) compared to Carbon fiber composite (CFRP), steel, and concrete:
Table 1 - Comparative list of properties of fiberglass composites, carbon fiber composites, steel A572, and concrete ||||| http://web.mit.edu/istgroup/ist/research/maglev.htm
As we can see in the chart above, Glass Fibers have a tensile strength of 1020 MPa, while steel only has a tensile strength of about 345 MPa. We can also see that the density of glass fibers is only 2.08 g/cm^3 (while steel has a very high density of 7.86 g/cm^3). This makes glass fibers a preferred material for high strength applications that require to be lightweight.
The high strength of the glass fiber composites come from the prevention of cracks mentioned above, as well as the strong covalent and ionic bonds within the ceramic. These bonds give it a very high yield strength, stiffness, and are also responsible for its brittle behavior.
There have been many tests on the health side effects of fiberglass by government agencies and private labs, with varying results. The generally agreed upon fact is that fiberglass is an irritant. When in contact with skin, fiberglass wool can cause skin irritation such as itchiness as well as redness and difficulty breathing and seeing. However, when fiberglass strands are embedded in a composite, fiberglass is no longer an irritant. Besides that there are no health concerns with fiber glass.
Picture Credit: http://betterwayproducts.com/wp-content/uploads/2012/02/fiberglass32inch2.jpg
Very high strength, low weight, low cost, relatively simple to manufacture, needs to be embedded in a raisin, very brittle. Great material!