Great zipper quality on this set. I've been using a variety of these compression packing cubes and they really help to minimize bulk in any suitcase. This set is made of thin-ish nylon. The top handles to grab and carry the bags are sturdy, as are the zippers. The compression zip goes all the way around twice, so it really does a nice job of flattening out the bag. You get a lot of size options with this set, the largest was big enough for 2 down vests, a down jacket and a pretty bulky wool cardigan.
This is my first time using this brand and their bags, I'll update the review on how they hold up after some use. (They seem pretty good during the initial pack up!)