What is the difference between 420D nylon bags or 600D polyester bag Which is cheaper and more durable?

In both cases, the "D" stands for the Word "denier", which is a measure of the fineness of the material. Specifically, the Word refers to the weight (in grams) of 9,000 meters of the fiber from which the material is made. In simpler terms, it means that a higher denier fabric is stronger and more durable than the same type of fabric with a lower denier rating. However, when comparing two different types of fabrics, such as polyester and nylon, it is important to note that because each fabric has different weights, 600D polyester fabric is not equal to 600D nylon fabric in terms of strength. In general, nylon is a stronger fabric type than polyester, and 420D nylon fabric, for example, is actually stronger than 600D polyester