The main ingredient in hair gels is a plastic called PVP, which is a polymer sealer. The polymers in PVP are dissolved in water or alcohol and form a clear film between each hair strand, attaching them to one another. Chemical experts call this “capillary power” because it’s similar to how blood capillaries work. When gel is applied to wet hair, the PVP or similar ingredient absorbs water quickly. When the gel dries completely, it forms a fixed connection between hair strands.