What Is Polyurethane-91?
Polyurethane-91 is a synthetic polymer that falls under the large family of urethanes. It begins life as a polyester made by reacting hexanediol with dimethyl carbonate. That polyester is then blended with 3-dimethylamino-1,2-propanediol and 1,4-butanediol, and the mixture is linked together with isophorone diisocyanate. Finally, the resulting polymer is neutralized with lactic acid, giving a stable, water-dispersible material that can be easily worked into skin-care formulas.
The rise of Polyurethane-91 in cosmetics traces back to the 1990s, when formulators started exploring lightweight polymers that could create smooth, flexible films on skin without the heavy feel of older resins. As consumer demand grew for long-lasting makeup and transfer-resistant skin-care products, Polyurethane-91 earned a place on ingredient lists thanks to its balance of comfort and durability.
Today you will commonly find Polyurethane-91 in liquid foundations, BB creams, tinted moisturizers, long-wear concealers, certain peel-off masks and even some hair-styling products. Its ability to form an invisible yet flexible film makes it useful in any formula that aims to stay put, resist smudging or deliver a smooth finish.
Polyurethane-91’s Cosmetic Benefits/Uses
In personal-care products Polyurethane-91 performs mainly one job, but it is an important one.
As a film forming agent, Polyurethane-91 creates a thin, breathable layer on the surface of skin or hair. This film helps makeup and skin treatments adhere better, improves water and sweat resistance, reduces transfer onto clothing and can give formulas a smoother, more even application.
Who Can Use Polyurethane-91
Polyurethane-91 is generally well tolerated across most skin types. Its lightweight breathable film makes it suitable for normal, combination and oily skin because it helps lock makeup in place without adding heavy oils. Dry skin can also use it, though those users will still need hydrating ingredients underneath since the polymer itself does not supply moisture. Sensitive or easily reactive skin usually handles Polyurethane-91 without trouble, but a tiny percentage of users may notice a tight sensation if multiple film formers are layered together.
The ingredient is entirely synthetic and sourced from petrochemical feedstocks, not animals, so it aligns with vegan and vegetarian lifestyles.
Current data shows no specific reproductive or developmental concerns associated with topical Polyurethane-91. The molecule is large and stays on the surface of skin, limiting systemic absorption. That said, this is not medical advice, and anyone who is pregnant or breastfeeding should run any skincare product past a qualified healthcare professional to be on the safe side.
Polyurethane-91 is not known to cause photosensitivity, so it will not make skin more prone to sunburn. Still, daily sunscreen is always recommended when spending time outdoors.
Potential Side Effects/Adverse Reactions
Side effects and reactions to the topical application of Polyurethane-91 can vary from person to person. The points below outline potential issues, but they are unlikely to represent the typical user experience. When the ingredient is formulated correctly most people will not encounter these problems.
- Mild skin irritation — a small number of users may notice redness stinging or itching, especially if skin is already compromised
- Contact dermatitis — very rarely an allergic-type reaction can occur leading to rash or swelling
- Increased breakouts — while non comedogenic for most, the film can occasionally trap sebum and debris on acne-prone skin which might contribute to clogged pores
- Difficulty removing product — the tenacious film could require thorough cleansing, and overly aggressive rubbing may provoke irritation
If any unwanted reaction develops stop using the product and consult a healthcare professional for guidance.
Comedogenic Rating
Rating: 1 / 5
Polyurethane-91 is a large, inert polymer that sits on the surface of skin without sinking into pores. It contains no fatty acids or oils that typically provoke clogging, so its inherent comedogenic potential is very low. The only reason it does not score a perfect zero is that the breathable film it creates can occasionally trap existing sebum and debris on highly acne-prone skin, which in turn might encourage a few extra blemishes if cleansing is inadequate.
Overall Polyurethane-91 is usually fine for people who break out easily, provided makeup is thoroughly removed at the end of the day.
If a formula pairs this polymer with heavy waxes or oils the finished product could feel more occlusive than Polyurethane-91 alone, so always consider the whole ingredient list when evaluating acne suitability.
Summary
Polyurethane-91 is used chiefly as a film former, meaning it dries down to a thin flexible layer that helps makeup and skin treatments stay put, resist water and look smoother. It achieves this by linking its urethane chains into a lightweight network that coats skin or hair without a heavy feel.
You will most often spot it in long-wear foundations, concealers, BB creams and the occasional peel-off mask. While popular within the niche of transfer-resistant cosmetics, it is not as widespread as mainstay silicones like dimethicone.
Safety data show it is non irritating for the vast majority of users, largely because the molecule is too big to penetrate living skin. Still, every complexion is unique, so patch testing a new product is always the smartest move before full-face use.