Hair typing is a classification system initially developed by Andre Walker. It uses the appearance of freshly washed hair to identify the hair's curl pattern, texture, density, porosity and elasticity.
The system is based on the notion that the hair's natural characteristics is most evident when it is freshly washed. The hair's curl pattern reflects the ability of the moisture to penetrate the hair shaft (porosity). The hair's elasticity or stretchiness describes how prone it is to breakage.
Hair that remains straight when wet falls into the type 1 category. Type 1 hair is resistant to curl styling, is noticeably shiny and ranges in texture from very fine (1A) to coarse (1C).
Hair that forms a gentle "S" wave pattern when wet is classified as type 2. This hair can be both straightened and curled with relative ease. Type 2 hair tends to have a fine density and sticks to the shape of the head.
Hair that forms spiral, corkscrew, and straw-sized curls is classified as type 3. This hair type can also be straightened and curled with relative ease. However, the high density and coarse textures of type 3 hair make it more prone to frizz.
Hair that becomes kinked or coiled when wet is identified as type 4. The curl pattern of type 4 hair ranges from curls the size of small crotchet needles (4A) to tightly kinked hair with no readily discernible pattern (4C). Type 4 hair can be curled and straightened, but is dense and very fragile. Its textures range from fine to coarse.