There are different academic views on the reasons for the high strength of fiberglass, and the main ones are as follows:

(1) Microcrack Hypothesis. It holds that glass has a high theoretical strength (2000-12000 MPa) depending on intermolecular gravity, but its measured strength is low due to microcracks of different sizes in glass or fiberglass, which cause stress concentration and reduce strength.

Surface microcracks are the most harmful. Fiberglass is stronger than glass because high-temperature molding reduces glass solution inhomogeneity and microcrack formation. Its small cross-section also reduces the probability of microcracks.

Thinner fiberglass has higher strength because it has fewer and smaller surface microcracks, thus reducing stress concentration effectively.

(2) Molecular Orientation Hypothesis. This hypothesis holds that during the molding process of fiberglass, the traction of the wire drawing machine makes the fiberglass molecules arranged directionally. This directional arrangement enhances the binding force between molecules, thereby significantly improving the strength of fiberglass.