Kaolin clay is sold in bulk form for many uses such as papermaking and pottery. Therefore, one might be inclined to think it is possible to save some money by purchasing cheaper bulk kaolin clay instead of paying for the same material labeled as Surround. However, the kaolin clay in Surround and the kaolin clay sold for other uses are really different materials using the same name. These attributes are essential to the way Surround functions. The finished product is hydrophilic instead of hydrophobic, and the mean particle size of Surround is much smaller than bulk kaolin clay, and just as importantly, the range of particle sizes is narrowed.
Particle size makes all the difference in how the particles affect insects.
Larger particles don't work. Surround has even shown promise as a suppressant against fire blight bacteria. Researchers have investigated kaolin clay since the 1930s as a foliar spray material, and have always had to contend with phytotoxicity. Home-brew concoctions of bulk kaolin clay can and have caused serious phytotoxicity on tree fruit and vegetable crops by starving the foliage of light. By controlling size, shape and porosity of the particles, Surround particles allow light rays within the range needed for photosynthesis to scatter and bounce their way down to the foliar surface.