The Plastic Boot — What Your Synthetic Wellies Are Actually Made Of

WATERPROOF FOOTWEAR TRILOGY — PART 1 OF 3 This series investigates what waterproof boots are made of and what they do to us. Part 1: The Plastic Boot (you are here) | Part 2: Wellington Boots | Part 3: The Waterproof Gap

Ninety percent in six months.

That is the proportion of DEHP—di(2-ethylhexyl) phthalate—that migrates out of a PVC wellington boot's sole within half a year of purchase.¹ It does not evaporate. It does not remain in the sole. It accumulates in the insole, the material pressed against your skin for eight hours a day if you wear boots for work, or all day if you are a child playing in puddles.

After one month of wear, the concentration in the insole rises from 0.³⁵ mg/g to 38-58 mg/g.¹ The material touching your feet becomes a reservoir of plasticizers approaching the concentration that was initially in the PVC itself.

The label on your boot will state "PVC" or "vinyl." It will not state "40% phthalates by weight."² It will not state "transfers endocrine disruptors to insole over time." It will not include a timeline of migration or a diagram of the pathway into your body.

This is what the label does not tell you.

The Chemistry

Flexible PVC products typically contain 40-70% phthalate plasticizers by weight.² The remainder is polyvinyl chloride polymer and trace amounts of stabilizers and pigments. The phthalates are what make the boot flexible. Without them, PVC is rigid—the material of pipes and window frames, not footwear.

The phthalates most commonly used in boots are DEHP, DBP (dibutyl phthalate), and increasingly DiNP (diisononyl phthalate).² DEHP, DBP, and related phthalates have been restricted in the European Union since July 2020 to a maximum of 0.1% by weight (cumulatively) in articles containing plasticized materials.³ DiNP is their replacement. According to Zota et al. (2014), DiNP increased substantially in the U.S. population between 2005 and 2010, precisely as DEHP declined.⁴

This is the pattern: one phthalate is restricted, another takes its place. The chemistry changes. The structure—a polymer matrix filled with plasticizers that are not chemically bound—remains the same.

Phthalates in PVC are not bonded to the polymer chain. They are trapped in cavities formed by the polymer, held only by weak intermolecular forces: van der Waals interactions, hydrogen bonds, electrostatic attraction.⁵ These are not permanent. According to Fick's law, the concentration gradient from the interior to the surface acts as the driving force for diffusion.⁵ Migration is not a manufacturing defect. It is thermodynamically inevitable.

The Migration

In 2022, researchers at the CSIR-CLRI in Chennai tracked what happens to DEHP in PVC shoe soles over six months.¹ They constructed footwear with PVC soles and leather insoles, simulating real-world wear under different environmental conditions. They measured phthalate concentrations at intervals.

The results were precise:

• Month 1: DEHP in the PVC sole decreased by 45-58%. The leather insole's DEHP concentration rose from 0.³⁵ mg/g to 38-58 mg/g.
• Month 6: About 90% of the DEHP had migrated out of the sole.

The migration was not linear. Roughly half of the DEHP left the sole in the first month, requiring five additional months for the remaining 40%. This suggests accelerated early migration—the period when boots are newest, when the "new boot smell" is strongest, when off-gassing is most active.

That smell is not inert. It is volatile organic compounds and semi-volatile organic compounds, including phthalates like DEHP, actively leaving the material.⁶ When you open a package containing a new PVC boot, shower curtain, or inflatable pool toy, the chemical odor you detect is proof of volatilization. The phthalates are mobile. The smell is the evidence.

Temperature accelerates this. The interior of a boot worn for hours in summer, or in warm climates, or during physical work, generates heat. The boot traps it. The migration accelerates.

The destination is the insole. Not the air. Not the environment outside the boot. The material in direct, prolonged contact with skin.

The Body Pathway

Phthalates enter the body through three primary routes: ingestion, inhalation, and dermal absorption. For footwear, the relevant pathway is dermal.

In 2015, researchers exposed six participants to diethyl phthalate (DEP) and di(n-butyl) phthalate (DnBP) in a controlled chamber for six hours.⁸ On one day, participants wore hoods and breathed filtered air, isolating dermal exposure. On another day, they breathed chamber air without hoods, allowing combined inhalation and dermal exposure. Urinary metabolites were measured over 48 hours.

The finding: "For both DEP and DnBP, both the dermal and inhalation pathways resulted in similar exposures."⁸

Dermal absorption is not negligible. For smaller phthalates, it is comparable to inhalation. For larger phthalates like DEHP, dermal permeation rates vary widely depending on study conditions, but the exposure scenario in footwear is not incidental contact. It is prolonged, daily contact with material containing 38-58 mg/g of DEHP after one month of wear.¹ Duration and concentration compensate for lower absorption rates.

Once absorbed, phthalates follow a consistent pathway:

• Skin → Bloodstream: DEHP is metabolized to MEHP (mono(2-ethylhexyl) phthalate) during and after absorption.¹⁰
• Bloodstream → Organs: MEHP circulates. It is further oxidized to metabolites including 5OH-MEHP and 5oxo-MEHP.¹⁰
• Organs → Urine: Most DEHP is excreted within 48 hours, primarily via urine.¹⁰

The half-life of MEHP in serum is approximately 2 hours initially, then 5 hours in a second elimination phase beginning 14-18 hours post-dose.¹⁰ For oxidized metabolites, the half-life is around 10 hours.¹⁰ DBP follows a similar pattern: over 90% is excreted via urinary metabolites within 48 hours.¹¹

This rapid excretion is sometimes cited by industry as evidence that phthalates "do not bioaccumulate."¹² It is true that phthalates do not persist in tissues for years. But rapid excretion does not prevent harm. It means that detectable levels in biomonitoring studies reflect ongoing, continuous exposure.

And exposure is ubiquitous. The U.S. Centers for Disease Control and Prevention's National Health and Nutrition Examination Survey (NHANES) detected phthalate metabolites in most Americans participating in the 2001-2010 cycles.⁴ Despite rapid metabolism and excretion, nearly the entire population carries measurable levels. This is not historical contamination. It is present-tense exposure.

The Evidence

In January 2026, the U.S. Environmental Protection Agency published final risk evaluations for five phthalates under the Toxic Substances Control Act: butyl benzyl phthalate (BBP), dibutyl phthalate (DBP), dicyclohexyl phthalate (DCHP), diethylhexyl phthalate (DEHP), and diisobutyl phthalate (DIBP).¹³

The EPA determined that these five phthalates "pose unreasonable risk to human health and/or the environment driven by specific conditions of use."¹³ For DEHP specifically, the agency found unreasonable risk to workers in 10 conditions of use and environmental risks in 20 conditions of use.¹³

The EPA did not find unreasonable risk to the general population from consumer products.¹³ This finding deserves scrutiny.

The TSCA risk evaluation scope is limited. It does not analyze exposures from food, food additives, food packaging, medical devices, cosmetics, or other consumer products under FDA or Consumer Product Safety Commission jurisdiction.¹³ The finding of "no unreasonable risk to consumers" applies to a subset of uses, not to cumulative exposure from all sources.

The agency did, however, find unreasonable risk to workers. Occupational exposure—prolonged, daily contact during manufacturing, processing, and use—exceeds safe thresholds. Many workers are required to wear occupational footwear for approximately 8 hours, 5 days a week.¹⁴ This is the same duration and frequency as a child wearing wellington boots to school daily, or an agricultural worker wearing PVC boots in fields.

The distinction between "worker" and "consumer" is a regulatory artifact. The exposure pathway is the same: prolonged dermal contact with phthalate-containing materials. The difference is documentation. Worker exposure is measured. Consumer exposure from footwear is not.

Children are particularly vulnerable. NHANES data from 2015-2018 show that children ages 6-10 had higher median levels of phthalate metabolites in urine compared to adolescents ages 16-17 and adults.¹⁵ Children have larger surface area-to-weight ratios, enhanced metabolic rates, and hand-to-mouth behaviors that increase exposure per kilogram of body weight.¹⁵ When children wore trousers, long-sleeved shirts, briefs, and socks simultaneously in one study, reproductive risks from phthalate exposure exceeded acceptable levels.¹⁶

A 2010 Danish EPA study found that plastic clogs and sandals made for both children and adults contained high levels of phthalates and concluded that the footwear "represent a significant contribution to the total phthalate exposure for consumers."¹⁴

The exposure is daily. The accumulation in insoles is progressive. The regulatory limit of 0.1% by weight assumes neither.³

The Comparison

This article is Part 1 of the Waterproof Footwear Trilogy. Part 2, Wellington Boots, documents natural rubber's environmental problems: vulcanization chemistry involving sulfur and accelerators, persistence in landfills exceeding 100+ years, and the gap between "natural" and "harmless."¹⁷ These problems are real.

But natural rubber formulations typically do not require phthalate plasticizers. The vulcanization process cross-links polymer chains using sulfur, fundamentally altering the molecular structure without the need for plasticizers.¹⁸ (Part 2 examines this chemistry in detail.) Natural rubber boots are heavier, stiffer, and more expensive than PVC boots. They degrade slowly in the environment. But they do not transfer endocrine disruptors to your skin.

The hierarchy of harm for body exposure is clear:

For environmental impact, the hierarchy inverts. Synthetic rubbers like neoprene and styrene-butadiene rubber (SBR) generate approximately 87-89% more CO2e per metric ton compared to natural rubber.²⁰ Natural rubber is renewable but persistent. PVC is neither renewable nor safe for the body.

This is not a choice between good options. It is a choice between harms. Natural rubber has environmental problems that Part 2 details. PVC has body exposure problems that this article documents. Synthetic rubber has both carbon intensity and chemical concerns, landing between the two.

If the question is "What touches my child's skin for eight hours a day?" the answer is: not PVC.

If the question is "What degrades in the environment?" the answer is: none of them do so safely within a human lifespan.

Part 3, The Waterproof Gap, asks whether sustainable waterproof footwear is even possible. For now, the hierarchy is weight-bearing: PVC is the worst option for the body. Natural rubber is the lesser evil. The label will not tell you this. The price will.

What the Label Does Not Tell You

The label tells you "PVC." It does not tell you "40-70% phthalates by weight."² It does not tell you that 90% will migrate from the sole to the insole within six months.¹ It does not tell you that the insole concentration will approach 38-58 mg/g after one month of wear.¹ It does not tell you that dermal absorption is a confirmed pathway.⁸ It does not tell you that DEHP is an endocrine disruptor or that the EPA found unreasonable risk to workers in similar exposure scenarios.¹³

It tells you the material class. It does not tell you what the material does over time or where the plasticizers go.

You now know what PVC boots are made of and what they do to your body. The boot you bought to keep water out is designed to transfer phthalates into the insole touching your skin. The chemistry is inevitable. The pathway is confirmed. The timeline is six months.

But before you choose an alternative, you need to understand what natural rubber actually is — and why "natural" does not mean "harmless." Part 2 of this trilogy examines that material.

WATERPROOF FOOTWEAR TRILOGY Part 1: The Plastic Boot (you are here) Part 2: Wellington Boots — Natural rubber's molecular contradiction Part 3: The Waterproof Gap — Is sustainable waterproof footwear even possible?