A suspension concentrate or flowable combines many of the characteristics of emulsifiable concentrates and wettable powders. The active ingredient in these formulations is usually a solid that does not dissolve in either water or oil. Although occasionally liquid active ingredients have been used but these must first be absorbed onto a solid carrier. The active ingredient, impregnated onto or combined with a substance such as clay, is ground to a very fine powder. The powder is then suspended in a small amount of liquid (usually water).
Other ingredients used in the formulation include; wetting agents, dispersants, viscosity modifiers (thickeners), preservatives and antifreeze.
The formulation is blended together with a hi-shear mixer and then liquid milled through a media mill using glass beads, zirconium oxide beads or sand as the grinding media. The mean particle size generated by this type of milling can be extremely small, often below 1 micron.
It is important that the active ingredient and any solid carriers used in this type of formulation have a very low solubility in the suspending solvent (usually less than 0.2%) otherwise Ostwald ripening (crystal growth) will occur in the product.
Flowables and liquids share many of the features of emulsifiable concentrates, and they have similar disadvantages. They often require moderate agitation to keep them in suspension and leave visible residues, similar to those of wettable powders. Flowables/liquids are easy to handle and apply. Because they are liquids, they are subject to spilling and splashing. They contain solid particles, so they contribute to abrasive wear of nozzles and pumps. Flowables can settle out in their containers if the particle size is too large or the viscosity is insufficient to maintain suspension. They require good shaking before pouring and mixing.