Why is glass fiber soft and tough

Glass is a hard and brittle material. However, as long as it is melted at high temperature, and then quickly pulled into very fine glass fibers through small holes, this material is very flexible. The same glass, why is the common block glass hard and brittle, while the fiber glass soft and tough? In fact, this can be well explained according to geometric principles.
Imagine bending a stick (assuming it is not broken), then different parts of the stick will be deformed to varying degrees, specifically, the outside is stretched, the inside is compressed, and the size of the axis is almost unchanged. When bending at the same angle, the thinner the stick is, the smaller the degree of external stretching is, and the smaller the degree of internal compression is. In other words, the thinner, the smaller the degree of local tension or compression deformation under the same bending degree. Any material can undergo a certain degree of continuous deformation, even glass is no exception, but the maximum deformation that brittle materials can withstand is smaller than that of ductile materials. When the glass fiber is thin enough, even if a large degree of bending occurs, its local tensile or compression deformation is very small, within the bearing range of the material, so it will not break.
It can be seen that the toughness and brittleness of materials are not absolute. The performance of a material is not only related to its internal composition and structure, but also to its scale. In addition, it is also related to factors such as force bearing mode. For example, many materials behave as fluid under very slow external action, and behave like rigid bodies under rapid external action. Therefore, when analyzing material properties, it is also necessary to consider the specific use or affected scenarios.