What type of twill fabric is known for a distinct diagonal rib and is commonly used for suits?

The type of twill fabric known for its distinct diagonal rib and commonly used for suits is gabardine. Gabardine is a tightly woven fabric that is durable and has a smooth texture, making it ideal for formal wear and tailoring. Its diagonal rib is a hallmark of twill weaves, resulting in a refined appearance that is often sought after for business attire.

The other fabrics listed, while they have their own unique characteristics, do not fit this description quite as precisely. Serge, for example, also has a twill weave and is used for suits, but it is less commonly known for the distinctive diagonal rib compared to gabardine. Tweed is typically a heavier wool fabric used for casual wear and outer garments, while denim, though it has a twill structure, is primarily associated with casual clothing and does not have the formal qualities needed for suits.