The little boy who brings his line to the old fishing hole uses a piece of cork as a “floater” without ever wondering what keeps that piece of cork bobbing on top of the water. But the capacity of cork to float has been known since ancient times, and cork life-preservers saved many a life thousands of years ago!

Cork is much lighter than water. The reason it floats is that water does not easily penetrate the walls of the cells, which are filled with air. This prevents the cork from becoming water-logged and sinking.

Cork is the outer bark of the cork oak tree. Two-thirds of the world’s cork supply comes from Spain and Portugal, where the cork oak is cultivated extensively.

The cork oak grows from 6 to 12 meters tall and can measure as much as 1 meter in diameter. The bark of this tree is usually first stripped when the tree is about 20 years old. This doesn’t injure or kill the tree; instead, the stripping actually benefits it.

About nine years later, another stripping is taken. The cork obtained from these first two strippings is coarse and rough. Later strippings, which are made about nine years apart for about a hundred years, give cork of a finer quality.

After stripping, the cork is stacked for several weeks to season, and then boiled to soften it and to remove the tannic acid. After boiling, the cork lies in pliable flat sheets, which are dried and then packed for shipping all over the world.

There are two kinds of raw cork: One is known as corkwood. This is the material used to make cork stoppers, floats, and life preservers. The second kind of raw cork is called grinding cork. It is ground up and then baked, some of it with binder materials. This is made into pipe covering, shoe fillers, automobile gaskets, and liners such as you find in the crown of bottle covers.

One of the greatest uses of cork today is for soundproofing rooms, and for insulating warehouses, freezer rooms, and refrigerators.