What Is Polyurethane-21?
Polyurethane-21 is a synthetic polymer made by reacting methylenedicyclohexanediisocyanate with small alcohol-based molecules such as 2,2-di(hydroxymethyl)propanoic acid, 2,2′-oxybisethanol and 2-oxepanone, then neutralizing the blend with tris(2-hydroxyethyl)amine. The finished material behaves like a flexible, water-dispersible plastic that dries into a clear film on skin or hair.
Polyurethane chemistry originated in the 1940s for industrial coatings. By the 1990s formulators noticed certain grades created breathable, comfortable films suitable for cosmetics. Polyurethane-21 was developed from that research and tailored to meet safety and sensory demands in personal care products.
Production starts in a closed reactor where the diisocyanate and diols link together, forming long chains in a process called polymerization. The mixture is then cooled, diluted with water and adjusted to a skin-friendly pH, yielding a milky liquid dispersion that blends easily into creams, gels or sprays.
You will find Polyurethane-21 in long-wear foundations, peel-off masks, water-resistant sunscreens, smudge-proof eyeliners and flexible hair styling products, all thanks to the thin durable film it creates.
Polyurethane-21’s Cosmetic Benefits/Uses
Polyurethane-21 has one primary function, but it brings multiple advantages to a formula.
As a film former it spreads into a uniform layer that holds pigments or actives in place, improves water and sweat resistance, provides a soft touch feel and offers a light tightening effect that smooths the look of skin. Its flexibility allows the film to bend with facial movements or hair styling without cracking so makeup and hair products stay fresh for longer wear.
Who Can Use Polyurethane-21
Polyurethane-21 suits most skin types including dry, normal, combination and oily because it forms a breathable flexible film that rarely interferes with the skin’s natural balance. Sensitive skin generally tolerates it well since the polymer is inert and free of common allergens, though anyone with a known sensitivity to polyurethane materials should stay cautious. Acne-prone users can usually apply it without fear of extra breakouts because the film is lightweight and non-occlusive, yet very reactive or congested skin might prefer minimal use until comfort is confirmed.
The polymer is synthesized entirely from petroleum-derived or laboratory-made components with no animal inputs so it is appropriate for vegans and vegetarians. No animal testing is required for its manufacture in regions that have alternative testing policies, though final product claims depend on the brand’s overall cruelty-free stance.
Current data shows no reproductive toxicity for topical use which means pregnant or breastfeeding women can ordinarily use products containing Polyurethane-21. This is not medical advice and anyone expecting or nursing should still clear every skincare product with a healthcare professional to be safe.
Polyurethane-21 does not make skin more sensitive to sunlight and has no known interactions with UV filters or self-tanning agents. It can even help water-resistant sunscreens stay put, boosting their performance during swimming or sweating.
Potential Side Effects/Adverse Reactions
Responses to topical Polyurethane-21 differ from person to person. The following points list potential but uncommon side effects when the ingredient is used in a correctly formulated cosmetic. Most people will not notice any of these issues.
- Mild skin irritation – a temporary feeling of dryness or tightness, especially if applied to very compromised skin
- Contact dermatitis – rare allergic rash for individuals hypersensitive to isocyanate-based polymers
- Eye stinging – possible if the raw dispersion accidentally drips into eyes before it sets
- Build-up on hair – repeated use in styling products may leave a film that needs clarifying shampoo to remove
- Heat rash or occlusion – prolonged heavy layers under hot humid conditions could trap sweat leading to small bumps
If any discomfort swelling or persistent redness occurs discontinue use and seek advice from a medical professional.
Comedogenic Rating
Rating: 1/5
Polyurethane-21 sits on the skin as a thin breathable film that allows water vapor to pass through rather than fully sealing pores. It has a large molecular size so it does not sink into follicle openings and it is used at low levels in finished formulas, all of which keep its clogging potential minimal.
Suitable for acne-prone and breakout-prone skin in most cases.
Formulas heavy in waxes or oils can raise the overall comedogenicity even if Polyurethane-21 itself is low so judge the whole product, not just this single ingredient.
Summary
Polyurethane-21 is a film former that locks pigments, sunscreen filters or styling resins into a flexible clear layer letting makeup last longer, sunscreen resist water and hair keep shape without crunch. It accomplishes this by drying into a micro-thin plastic network that bends with movement so it resists cracking or flaking.
While not as famous as silicones or acrylates it is gaining traction in long-wear makeup and sporty suncare because consumers want durability with a light feel.
Current safety data shows very low toxicity for topical use, rare irritation and no photo-reactivity. Even so every person’s skin is unique so it is wise to patch test any new product that contains Polyurethane-21 before full application.