Penetrants dissolve or penetrate waxy layers on leaves and allow other chemicals to interface with plant cells or insect epidermal tissue and enter the spaces between the epidermal cells, sometimes called “cell free space.” Penetrants can contain petroleum by-products, crop oils, complex alcohols, and other hydrocarbon-based materials. They work well under very specific conditions and with very specific crops grown outdoors. In the greenhouse, stand-alone products are rare.