Kapok is a light, buoyant down. It is composed of fine white or usually light colored, smooth, hairlike fibers about an inch long. These fibers are single cells with thin walls completely closed around a central cavity. Each individual fiber is therefore a miniature gas bag. Unlike nearly all other fibers and plant tissues, the cell walls do not absorb moisture. Water can not enter the cells unless the walls are broken.

The allied fibers, pochote, semul, samohu, paina, samauma, and others from other trees of the same family as kapok, are all of similar structure, varying in length, luster, and the thickness of the cell walls.

All of these fibers are produced in the seed pods of trees belonging to the Bombax family. They grow on certain portions of the inner walls of the seed pods and to a less extent on the seeds, but in most species at maturity both seeds and down are entirely free from any attachment.

Practically all of the fiber or down of this class entering commerce heretofore has consisted of kapok from the randoe tree, Ceiba pentandra indica, of Java and the Philippines, and semul from the red semul tree, Gossampinus heptaphylla, of India. There are 54 different species of trees belonging to 4 genera of the Bombax family now known to yield fiber of this class, and others are being discovered as new areas are explored. These now known include 11 species of the genus Ceiba, ranging from northern Mexico to Brazil, with Ceiba pentandra, cultivated for the production of kapok, widely distributed in the tropics of both hemispheres; 25 species of Bombax, chiefly in Brazil, but some extending to southern Mexico and 1 in tropical Africa; 7 of Chorisia, confined chiefly to the La Plata region in South America, and 11 of Gossampinus, in southern Asia and tropical Africa. All are native in tropical or subtropical countries. Some are known to yield down fully equal in quality to the kapok now on the market. Kapok has been produced most extensively and with the greatest care in Java; but with the same care in picking the seed pods, cleaning the down, and in grading, inspecting, and marketing, just as good down may be produced in other tropical countries.

FIGURE 132.—Kapok seed pod and seeds. The down grows on the inner walls of the seed pods and less on the seeds, but when mature and dry neither down nor seeds have any attachment

Not Textile Fibers

These are not textile fibers, for they do not cling together so as to make a strong yarn. Their valuable properties are resiliency, buoyancy, and resistance to transmission of heat. In each of these properties their value is diminished if the fibers are crushed or broken.

Because of their resiliency they are used in mattresses, pillows, and upholstery. Because of their buoyancy, greater than that of cork, they are used in life preservers. Because of their resistance (kapok now heading the list of tested temperature insulators) their use is increasing in refrigerators, refrigerator cars, trucks for distributing ice cream, and for many purposes where efficient heat insulation is required.