The most basic three-ring binder is a simple plastic binder with two inside pockets and three open-and-close rings. This type of binder is best for students who don't need to carry all of their items with them in one binder, or students who have multiple binders for multiple subjects. These types of binders are typically the most inexpensive, and come in many different colors. Plastic three-ring binders also come in numerous different spine widths, which is important to consider when you're factoring in them being able to hold a certain amount of paper.
Zipper binders, also know as trapperkeepers, are similar in construction to the basic plastic three-ring binder, with the major differences being a softer material used for the covering and a zipper enclosing the binder. Zipper binders are more expensive, but offer benefits such as more space for papers and folders, no sharp edges (ideal for younger children) and a zipper that keeps important items from falling out. Zipper binders also offer greater design variety, and come with all kinds of fun patterns on their covers and insides.
Expandable binders are a step up from the classic zippered binder. Expandable binders offer unmatched space capacity, as they can expand to meet the need for more space. You can find simple plastic expandable binders, which expand the spine of the binder, as well as more-complex, zipper-style expandable binders, such as the Five Star Xpanz 2-inch Zipper Binder by Mead and the Case-It Build-A-Binder Neoprene Zipper Binder. Many expandable binders include a shoulder strap or a handle to make them easier to carry.
Z-Binders are a recent addition to the binder market, and offer a unique design unlike the typical three-ring binders that have been on the school supply market for so long. Z-Binders fold out into a Z shape, creating two binders worth of space in one. Z-Binders, such as the Case-it Z-Binder 2-in-1 Zipper Binder, are perfect for organizing multiple subjects while still keeping all your important papers and items close at hand.