Why is one of the most ubiquitous supplies in the office called a "Manila" folder?

Now one would not typically associate the capital of the Philippines for being an business powerhouse - that is usually reserved for cities such as New York City or London.  Yet one of the most common office supplies found in law offices, financial institutions and doctors' clinics is the "Manila" folder.

So why is it called that?

Originally, these folders were constructed from Manila hemp.  This is a type of fiber obtained from the abaca - a relative of the banana.  Being the tropical climate that it is, the abaca is a common product of the Philippines and as such, was exported and used extensively to make the folders that bear its name to this day.