I believe that the number (1050 etc) is mass in grams of 9000 meters of thread. That is why B&R is to a first approximation, indestructible and why it is such a great value compared to say Tumi, which uses lighter fabric. There are some issues with the 1600 denier however with abrasion compared to the 1050. The 1050 was the original Dupont ballistic nylon. The name was because they had intended it to be bulletproof. It wasnt. It is also why B&R is heavier, and one could argue that it is overkill and not worth the weight. Opinions vary on that, even in my case, within the same person

Also, on a per weight basis many think that the 1050 is the best. Dupont Cordura (1000 denier) is a newer fabric that is generally considered slightly superior to 1050D although it apparently has some properties not as good as 1050D. Red Oxx uses Cordura. In addition to weight of the fabric, there are of course differences in the quality based on who makes it. I actually think that B&R should continue to use the 2520D in their rollers and switch to 1050D or Cordura in their hand carry bags. Also, I think that the D and the end is for Dupont, who makes the best ballistic nylon.

There is a discussion comparing Cordura and 1050D on this bulletin board with a post from.... Tom Bihn himself.