What Is Polyurethane-18?
Polyurethane-18 is a man-made polymer that forms when butanediisocyanate reacts with special kinds of alcohols called polyols, plus small amounts of 2,2-di(hydroxymethyl)propanoic acid. The mix is neutralized with tris(2-hydroxyethyl)amine then further linked with hydrazine or short alkanediamines. The result is a flexible yet durable film-forming material that dissolves or swells in water-based formulas.
Polyurethanes started showing up in everyday products during the 1940s as lightweight foams and coatings. Cosmetic chemists later noticed that certain grades could create clear, flexible films on skin and hair, so in the late 1980s and early 1990s they adapted them for styling sprays and long-wear makeup. Polyurethane-18 is one of these newer grades, optimized to work well in water and alcohol systems without feeling stiff or sticky.
Manufacturing involves carefully controlled, computer-guided reactions to ensure that no unreacted isocyanate remains. The finished polymer is filtered, dried into a powder or supplied as a 30-40 % solution then shipped to cosmetic labs ready to use.
You will most often see Polyurethane-18 in hair sprays, styling gels, brow setters, long-wear eyeliners, liquid lipsticks, waterproof mascaras and transfer-resistant foundations. Its ability to form thin flexible films also makes it handy in peel-off masks and nail treatments.
Polyurethane-18’s Cosmetic Benefits/Uses
Formulators turn to Polyurethane-18 because it performs two main jobs that improve how a product looks, feels and lasts on the body
- Binding: The polymer acts like a glue that keeps pigments, shimmer particles and other ingredients evenly dispersed so a formula stays uniform in the bottle and delivers consistent color or coverage on application
- Hair fixing: Once dry it forms a lightweight film around hair fibers that locks a style in place, fights humidity and adds a touch of shine without flaking or weighing hair down
Who Can Use Polyurethane-18
Polyurethane-18 is considered suitable for all skin types, including dry, normal, combination and oily skin, because the polymer forms a breathable film that does not noticeably clog pores or strip moisture. Extremely sensitive or allergy-prone skin may wish to proceed carefully, as any synthetic polymer can occasionally provoke irritation in those with compromised barriers.
The ingredient is fully synthetic and contains no animal-derived raw materials, so it is generally accepted by vegan and vegetarian consumers.
No specific contraindications have been flagged for those who are pregnant or breastfeeding. The polymer is not known to penetrate deeply or act systemically, yet this is not medical advice and anyone expecting or nursing should ask a healthcare professional before adding new cosmetic products.
Polyurethane-18 does not absorb UV light and is not associated with photosensitivity. It also plays well with common actives such as acids, retinoids and vitamin C, making it a flexible option in layered routines.
Potential Side Effects/Adverse Reactions
Reactions to topical Polyurethane-18 vary from person to person. The following list covers potential side effects, but most users will not experience them when the ingredient is correctly formulated and used as directed.
- Mild skin irritation, redness or itching in very sensitive individuals
- Contact dermatitis triggered by trace residual monomers or solvents if purification was incomplete
- Eye stinging or watering if aerosol styling sprays are inhaled or drift into the eyes
- Scalp or hair buildup leading to dullness if cleansing is inadequate after heavy styling product use
If any discomfort, rash or other unexpected reaction occurs, stop using the product and seek advice from a healthcare professional.
Comedogenic Rating
Rating: 1/5. Polyurethane-18 is a large water-dispersible polymer that sits on top of skin in a thin breathable film rather than sinking into follicles. It contains no oily or waxy fractions that typically trigger clogged pores, and it is easily washed off with regular cleansing. Because of this low likelihood of pore blockage it is generally suitable for people prone to acne or breakouts.
One thing to keep in mind is that formulas using heavy emollients alongside Polyurethane-18, such as rich creams or pomades, could still feel occlusive and cause congestion in very oily skin. In those cases the overall formula, not the polymer itself, would be the main concern.
Summary
Polyurethane-18 serves two key roles in cosmetics: it binds pigments and other particles so products stay uniform, and it creates a flexible humidity-resistant film that sets hair or makeup in place. These benefits stem from its long chain structure that interlocks as it dries, giving smooth hold without stiffness.
The polymer is moderately popular in styling sprays, brow gels and long-wear makeup where clear lightweight hold is prized, but it is still less common than older resins like PVP because it costs more and requires specific processing.
Safety data and real-world use show Polyurethane-18 to be low risk for irritation, sensitization or comedogenicity when properly formulated. As with any new cosmetic it is smart to patch test first if you have reactive skin or known allergies.