What Is Polyester-31?
Polyester-31 is a man-made polymer created when several small molecules, including diethylene glycol, glycol, neopentyl glycol, isophthalic acid, sebacic acid and terephthalic acid, are linked together in a controlled reaction. The result is a stable film-forming resin that behaves much like a flexible plastic once it is dissolved or dispersed in a cosmetic base.
Chemists first explored this type of polyester in the late twentieth century while searching for lightweight alternatives to heavy waxes and gums. Its ability to spread easily, survive heat during manufacturing and leave a smooth finish made it a natural fit for personal care labs. Over time formulators learned that Polyester-31 could replace multiple raw materials at once, giving brands a way to simplify ingredient lists while keeping products pleasant to use.
The manufacturing process starts with heating the glycols and acids in large reactors. Water that forms during the reaction is removed so the molecules can keep joining together, building long chains. When the target molecular weight is reached the hot mixture is cooled, chipped and then ground into a fine powder or melted into pellets that ship to cosmetic factories.
Today you will most often spot Polyester-31 in facial masks, long-wear makeup, hair styling creams, skin primers, sunscreens, body lotions and leave-on conditioners. It is prized for giving products a soft, flexible film that holds pigments, actives and moisturizers right where you want them.
Polyester-31’s Cosmetic Benefits/Uses
Formulators choose Polyester-31 for two main technical roles that translate into user-friendly benefits.
- Binding: Helps powders, colorants and other particles stick together so the formula does not separate in the jar or on the skin. This keeps makeup even, prevents streaks in lotions and lets active ingredients stay evenly distributed for consistent results.
- Film forming: Creates a thin breathable layer on skin or hair that locks in moisture, boosts shine and improves wear time. The film resists sweat and water yet washes away with normal cleansing, making products feel light while lasting longer through daily activities.
Who Can Use Polyester-31
Polyester-31 is considered friendly for most skin and hair types. Its lightweight film is non occlusive so it suits oily and combination skin while still helping dry skin hold moisture. Very sensitive or reactive complexions can usually tolerate it, though anyone with a known sensitivity to polyester resins should proceed carefully.
The ingredient is synthesized entirely from petrochemical or plant derived lab reagents with no animal inputs, making it acceptable for vegans and vegetarians.
Because the polymer molecules are large and sit on the surface rather than penetrating, they are not expected to enter the bloodstream. Current safety assessments list no specific concerns for pregnant or nursing women, yet this is not medical advice. Anyone expecting or breastfeeding should show the full product label to a qualified physician before use just to be safe.
Polyester-31 does not absorb UV light and is not associated with photosensitivity. It also plays well with common actives like retinoids, vitamin C or acids, so routine daytime SPF rules apply but no extra precautions are needed.
Potential Side Effects/Adverse Reactions
Responses to topical Polyester-31 vary from person to person. The following is a list of potential side effects, all of which are unlikely for the average user when the ingredient is formulated and applied as directed.
- Mild skin irritation such as temporary redness, itching or a stinging sensation
- Contact dermatitis in individuals allergic to polyester resins or related chemicals
- Follicular buildup that may contribute to clogged pores in very acne prone skin if heavy layers are not removed thoroughly
- Scalp or hair residue leading to dullness when used in leave on styling products without regular cleansing
If any discomfort or unusual reaction occurs stop using the product and consult a healthcare professional or dermatologist for guidance.
Comedogenic Rating
Comedogenic rating: 1 out of 5. Polyester-31 forms a thin breathable film that contains very little oil so it rarely blocks pores. Because any film former can trap debris if layered heavily or left on overnight the score is kept just above zero.
Generally considered suitable for people prone to acne or breakouts.
If you live in a hot humid climate or wear multiple long-wear products a thorough evening cleanse will help prevent buildup.
Summary
Polyester-31 works by binding powders pigments and actives into a uniform mix then creating a flexible surface film that locks them in place, resists sweat and helps skin or hair retain moisture. This gives products longer wear without a heavy feel.
Although appreciated by formulators for its versatility it remains a specialty polymer so it shows up mainly in long-wear makeup, sunscreens and advanced hair care rather than everyday basics.
Safety reviews rate it low risk with minimal irritation or pore-clogging potential. Still, anyone trying a new product that contains Polyester-31 should do a quick patch test first to be sure it agrees with their skin.