What characteristic is true about fiberglass fillers?

Fiberglass fillers are known for their waterproof characteristics, which makes them particularly suitable for applications where moisture resistance is essential. Waterproofing is a significant benefit because it helps prevent water infiltration, which can lead to rusting and deterioration of both the filler itself and the underlying materials being repaired, such as metal or wood. This attribute allows fiberglass fillers to be used effectively in a variety of environments, including areas that are exposed to high humidity or direct water contact.

Additionally, the composite structure of fiberglass fillers, typically integrating resin with fiberglass strands, contributes to their durability and resilience. This aspect further supports their use in auto body repair, where the longevity and integrity of repairs are critical.

In contrast, characteristics such as being porous and non-waterproof do not apply to fiberglass fillers, as these qualities would undermine the effectiveness of the filler in automotive applications. Being brittle is also not a defining trait of fiberglass fillers; instead, they are generally designed to be flexible enough to adhere well to various substrates without cracking under stress.