PDMS, or polydimethylsiloxane, is a silicon-based synthetic polymer that belongs to the silicone family. It’s one of the most versatile materials in modern manufacturing, showing up in everything from your shampoo and cooking oil to breast implants and lab-on-a-chip devices. You may also know it by its cosmetic name, dimethicone, or its European food additive number, E 900. Its unusual combination of flexibility, transparency, and biological safety makes it useful across a remarkably wide range of industries.
Chemical Structure and Basic Properties
PDMS is built on a backbone of alternating silicon and oxygen atoms, with two methyl groups (small carbon-hydrogen clusters) hanging off each silicon. The repeating unit is Si(CH₃)₂O, and these units chain together into long, flexible strands. This silicon-oxygen backbone is what distinguishes silicones from carbon-based plastics and gives PDMS many of its defining traits.
The material is optically clear, with a refractive index of 1.4, close to that of glass. It behaves as a viscoelastic material, meaning it can flow like a thick liquid in its uncured form but bounce back like rubber once it’s been cross-linked (hardened). It’s hydrophobic, so water beads up on its surface rather than soaking in. It stays stable across a wide temperature range, resists UV light, and is permeable to gases like oxygen, which turns out to be critical for certain biomedical applications.
How PDMS Is Made
PDMS starts as a liquid. To turn it into a solid, rubbery material, manufacturers cross-link the polymer chains so they form a three-dimensional network instead of sliding past each other. The most common method is addition curing, where two liquid components are mixed together. Part A contains the silicone base with a platinum catalyst, and Part B contains the cross-linking agent. When combined, they react and gradually harden into a flexible solid.
The ratio of these two parts controls the final material’s stiffness and density. More cross-linking agent produces a denser, stiffer result. Curing typically requires heat (around 80°C) and can take many hours depending on the application. This two-part system is what makes PDMS so easy to work with: you can pour the liquid mixture into a mold of virtually any shape, then cure it into a precise, detailed replica.
Uses in Cosmetics and Personal Care
On ingredient labels, PDMS appears as “dimethicone,” and it’s one of the most common ingredients in skincare, haircare, and color cosmetics. In moisturizers, it acts as an occlusive agent, forming a thin, non-greasy barrier on the skin that locks in moisture without feeling heavy. It also works as an emollient, smoothing the skin’s surface by filling in microscopic gaps where damaged skin cells are missing.
In hair products, dimethicone is the workhorse behind most conditioners. It coats individual hair fibers, reducing friction between them and creating the slip, shine, and smoothness people associate with well-conditioned hair. In makeup, silicones serve as spreading agents for pigments. They glide easily across skin, then evaporate, leaving behind an even film of color. This is why silicone-based primers feel so distinctively smooth on application.
Uses in Food
PDMS is authorized as a food additive in the European Union under the designation E 900, primarily as an anti-foaming agent. When oils are heated for frying, or when juices, soups, and flavored beverages are processed at scale, unwanted foam can form. A tiny amount of PDMS prevents this. Maximum permitted levels range from 10 mg/kg in most food categories (frying oils, canned fruits and vegetables, soups, batters, jams, confectionery) up to 100 mg/kg in chewing gum. It’s also permitted in fruit glazes and as an additive in food colorings and flavorings at very low concentrations.
Medical and Biomedical Applications
PDMS is biocompatible, meaning the body generally tolerates it without a strong immune reaction. This property has made it a go-to material for implantable medical devices. Both saline-filled and silicone gel-filled breast implants use PDMS shells and are classified as Class III devices by the FDA, the highest regulatory category requiring the most rigorous review. Other Class III silicone-based devices include inflatable penile implants, implanted urinary continence devices, and certain neuromodulatory systems.
Beyond implants, PDMS is the dominant material in microfluidics, a field that builds tiny channels on chips to manipulate small volumes of fluid for medical diagnostics, drug testing, and biological research. The vast majority of these “lab-on-a-chip” devices are molded from PDMS using a technique called soft lithography, where liquid PDMS is poured over a patterned template and cured. Researchers favor it because it’s transparent (so you can observe what’s happening inside the channels), elastic, gas-permeable (allowing oxygen to reach living cells inside the device), and inexpensive compared to alternatives like glass or silicon wafers.
Environmental Breakdown
PDMS enters the environment mainly through wastewater treatment. It ends up in sewage sludge, which is sometimes spread on agricultural soil as a fertilizer. Once in contact with dry soil, PDMS breaks down through hydrolysis into smaller silicone units that either biodegrade further or evaporate.
How fast this happens depends heavily on climate. USDA modeling across multiple U.S. locations found that over 95% of PDMS applied to soil surfaces degraded within one year in areas with good drying conditions, like Puerto Rico and Georgia. In cooler, wetter climates like Ohio, degradation was slower, and in some years more than 50% of the applied PDMS remained at shallow depths after a full year. Two years after sludge application, predicted concentrations in the top 10 cm of soil dropped to about 19.8 mg per kilogram of soil. The key factor is soil moisture: drier soils promote faster breakdown, while persistently wet soils slow the process considerably.