Resealable bags provide a convenient way to store leftover food. It's easy to overlook the ingenuity of plastic resealable bags, but these bags have become an everyday item in households the world over.

Resealable plastic bags are a relatively new invention, in fact they've only been around for about 50 years. The resealable plastic bag was originally patented as a pencil bag in 1954. A fifth grader came up with the idea that you could use these 'pencil bags' to retard food spoilage and store food. By 1968 Ziploc bags were fully developed and patented. The brand now synonymous with resealable bags is Ziploc, and the company is now worth over $1 billion.

The bag consists of a seal at the top so that the plastic bag can be easily sealed and reopened. The bag locks in freshness, so that food remains fresher for longer. In this way resealable bags are similar to Tupperware. The bags are commonly used by mothers for school lunches for their children.

Resealable bags are also available to freeze food in. These are called freezer bags. Freezer bags are convenient for separating out portions of food and keeping some of it frozen, whilst you use the other portion. The fact that these bags can be easily opened and resealed means that people can easily portion out food as they need it and keep the remainder frozen.

Another type of resealable plastic bag is the expandable bottom bag, which is able to stand on its own. These bags are great for storing liquid in. They can also be used to store non-food products in, such as oil, perfume and medicine.

Since Ziploc bags were developed at the same time as the microwave, and became domestically used at about the same time, it makes sense that there are resealable bags for the microwave. These bags allow you to steam food in the microwave, and they can even be cleaned and reused.

Thanks to their flexible usage properties; their reusable quality; and their affordable pricing, resealable bags have become one of the most successful products of the twentieth century.