What Is Polyurethane-45?
Polyurethane-45 is a synthetic polymer created by reacting epsilon caprolactone and trimethylolpropane with the cyclic trimer of hexamethylene diisocyanate. The result is a flexible lattice of repeating urethane links that dries to form a clear breathable film on the skin. Polyurethanes were first developed for industrial coatings in the 1940s, and cosmetic chemists began adapting them in the 1990s when lighter non-tacky variants like Polyurethane-45 became available. Manufacturing starts with the controlled ring-opening polymerization of epsilon caprolactone around a trimethylolpropane core, followed by coupling with the diisocyanate trimer to lock in durability and water resistance. After neutralization and purification the material is supplied as a water-dispersible resin or fine powder that blends easily into personal care formulas. You will most often find Polyurethane-45 in long-wear makeup such as foundations, eyeliners and mascaras, transfer-resistant lip colors, flexible hold hair stylers, facial masks that peel off cleanly as well as tinted moisturizers that claim all-day wear.
Polyurethane-45’s Cosmetic Benefits/Uses
In beauty products Polyurethane-45 serves one principal role that delivers several practical advantages.
Film forming: Once applied and allowed to dry the polymer creates a thin uniform film that improves the adherence and longevity of pigments and active ingredients, resists smudging from sweat or sebum, adds water resistance for better wear during humid conditions or light water exposure, and imparts a smooth flexible finish that moves comfortably with facial expressions without cracking or flaking.
Who Can Use Polyurethane-45
Polyurethane-45 suits most skin types. Its breathable film is light enough for normal, dry and combination skin while still helping oily complexions keep makeup in place. Very sensitive or eczema-prone users generally tolerate it well because the polymer sits on the surface rather than penetrating deeply. The only caveat is that extremely oily or acneic skin might feel a slight buildup if several layers of long-wear products containing the resin are applied at once.
The ingredient is fully synthetic with no animal-derived raw materials so it is considered suitable for vegans and vegetarians.
Because Polyurethane-45 is a large inert molecule that is unlikely to cross the skin barrier it is not expected to pose a risk during pregnancy or while breastfeeding. This is not medical advice and anyone who is pregnant or nursing should review all personal care products with a healthcare professional to be safe.
Polyurethane-45 does not increase photosensitivity and can be used alongside daily sunscreen without additional sun-related precautions. It is also fragrance-free and dye-free so it rarely clashes with other actives or treatments.
Potential Side Effects/Adverse Reactions
Responses to topical Polyurethane-45 differ from person to person. The following list covers potential but uncommon reactions when the ingredient is used as directed in finished cosmetics. Most users will not experience these issues.
- Mild skin irritation or redness, usually linked to very sensitive skin
- Itchiness or tight sensation if the film is applied too thickly
- Watery eyes or stinging when used around the lash line in people who are prone to ocular sensitivity
- Temporary clogged pores if layered with heavy occlusive products on oily skin
- Allergic contact dermatitis triggered by trace residual monomers in extremely rare cases
If any discomfort or reaction occurs stop using the product immediately and consult a qualified healthcare professional.
Comedogenic Rating
Rating: 1/5 (low likelihood of clogging pores)
Polyurethane-45 forms a breathable lattice that sits on top of the skin rather than seeping into pores. It contains no oils or fatty acids that feed acne-causing bacteria, and the finished film allows normal water vapor transmission so it is unlikely to trap excessive sebum underneath. That said, very oily skin types could notice a slight buildup if they layer several long-wear products containing the polymer without thorough cleansing.
Overall Polyurethane-45 is considered suitable for people who are prone to breakouts and is rarely linked to acne flare-ups.
Formulators sometimes combine the resin with waxes or heavy silicones to boost wear time; in those blended formulas any pore-clogging potential usually comes from the other ingredients, not the polyurethane itself.
Summary
Polyurethane-45 is a synthetic film former prized for its ability to create a thin flexible shield that locks pigments in place, boosts water and smudge resistance, and leaves a smooth comfortable finish. By polymerizing caprolactone, trimethylolpropane and a hexamethylene diisocyanate trimer, chemists produce a large inert molecule that dries quickly yet remains breathable so makeup lasts longer without cracking or migrating.
While not as widely recognized as silicones or acrylates, the ingredient has carved out a niche in long-wear foundations, mascaras, peel-off masks and flexible hold hair products where durability matters most. Its popularity is growing as brands seek lighter non-tacky alternatives to older film formers.
Safety data show Polyurethane-45 is generally well tolerated, vegan friendly and pregnancy safe when used in finished cosmetics. As with any new product though, it is wise to perform a brief patch test on a small area of skin to rule out personal sensitivities before full application.