Primer is made of four core ingredients: resins (binders), solvents, pigments or fillers, and additives. That applies to paint primer specifically, which is what most people mean when they search this question. Makeup primer uses a different formula built around silicones or water-based polymers. Both types share the same basic job: creating a smooth, grippy surface for whatever goes on top.
The Four Main Ingredients in Paint Primer
Every paint primer is a mixture of the same four categories of ingredients, adjusted depending on the surface it’s designed for and whether it’s oil-based or water-based.
Resins (binders) are the backbone of any primer. These are polymers that hold everything together once the primer dries, binding pigment particles into a solid film and anchoring that film to the surface underneath. The three most common resin types in primer are acrylic, alkyd, and epoxy. Acrylic resins are standard in water-based primers. Alkyd resins, derived from plant oils, are found in oil-based primers and cure by reacting with oxygen in the air. Epoxy resins show up in heavy-duty primers for metal and concrete where chemical resistance matters.
Solvents keep the primer liquid so you can spread it. In water-based (latex) primers, the solvent is simply water. In oil-based primers, the solvent is typically mineral spirits, a petroleum-derived liquid that evaporates slowly and carries less fire risk than faster solvents like acetone. As the solvent evaporates, the resin and pigment are left behind as a dry film. This evaporation is what people mean by “drying time,” and it’s why oil-based primers take longer to dry and produce stronger fumes.
Pigments and fillers give primer its color and hiding power. Titanium dioxide is the most common white pigment, valued for its exceptional ability to block whatever color is underneath. It has one of the highest refractive indexes of any pigment, which is why primer can cover dark surfaces so effectively. Calcium carbonate (essentially ground limestone) and talc are used as cheaper fillers that bulk up the primer, improve sandability, and create a slightly rough surface texture that helps the topcoat grip.
Additives are the smaller ingredients that solve specific problems. Biocides prevent bacteria and mold from growing inside the can during storage. Defoamers, often blends of mineral oils and silica compounds, keep bubbles from forming as you brush or roll the primer on. Surfactants reduce surface tension so the primer wets and spreads evenly instead of beading up. Some primers also contain anti-gelling agents that keep pigments from clumping together over time.
How Primer Bonds to a Surface
Primer works differently than regular paint at the molecular level. When you apply primer, the resins are adsorbed onto the substrate, forming chemical bonds with the surface material and creating a thin, tightly attached layer. This is why primer sticks to bare wood, metal, or drywall better than paint alone would. Paint is formulated to look good on top. Primer is formulated to grab what’s below it and give paint something to hold onto above it.
The pigments and fillers also play a role in adhesion. They create a slightly porous, textured surface (sometimes called “tooth”) that gives the topcoat more area to grip. This is why sanding a glossy surface before priming helps so much: you’re creating the same kind of micro-texture at the substrate level that primer creates for paint.
How Oil-Based and Water-Based Primers Differ
The biggest compositional difference is the solvent. Oil-based primers use mineral spirits and alkyd resins, which produce a harder, more moisture-resistant film. They’re better at sealing stains, tannin bleed from wood, and odors, but they take longer to dry and release more volatile organic compounds (VOCs) as the mineral spirits evaporate.
Water-based primers use acrylic resins suspended in water. They dry faster, clean up with soap and water, and produce far fewer fumes. Modern acrylic primers have closed much of the performance gap with oil-based options, but oil-based primers still hold an edge on raw wood, heavy stain blocking, and metal surfaces exposed to moisture.
Metal Primer Has Extra Corrosion Protection
Primers designed for steel and iron contain corrosion-inhibiting pigments that regular primers don’t. Zinc phosphate is the most widely used, a white powder that forms a protective barrier between the metal and moisture. It has largely replaced older inhibitors based on lead and chromium, which were effective but toxic. By 2006, zinc phosphate had become the most commonly used corrosion inhibitor in primer coatings. Some industrial metal primers also contain metallic zinc dust, which sacrificially corrodes in place of the steel underneath.
What Makeup Primer Is Made Of
Cosmetic primer shares the same goal as paint primer (creating a smooth base for what goes on top) but uses completely different chemistry. The two main categories are silicone-based and water-based.
Silicone-based primers rely on ingredients like dimethicone and cyclopentasiloxane, which create a slippery, velvety film that fills in fine lines and pores. A typical silicone primer might be nearly 30% silicone compounds by volume, with water and humectants like propylene glycol making up most of the rest. These silicones are what give the primer that distinctive smooth, almost rubbery feel when you rub it between your fingers.
Water-based primers use film-forming polymers and hydrating ingredients instead. They tend to list water as the first ingredient followed by glycerin, hyaluronic acid, or plant-derived extracts. You can usually identify a silicone-based primer by looking for words ending in “-cone,” “-methicone,” or “-siloxane” near the top of the ingredient list. If those appear far down the list or not at all, the primer is water-based. Matching your primer type to your foundation type (silicone with silicone, water with water) helps both layers blend together instead of pilling or separating on your skin.