If you've spent time reading formula labels, the bottle deserves a second of the same attention. Plastic baby bottles release microplastics into formula, and the volumes involved aren't trivial. Glass changes that, and the change is one of the simplest material swaps you can make.
"We were absolutely gobsmacked. Adults consume an estimated 300–600 microplastics a day. Our values for infants were on the order of a million."
Prof. John Boland · Trinity College Dublin · Nature Food, 2020
The estimated number of microplastic particles an average infant ingests each day when fed from a standard polypropylene bottle , following WHO-recommended preparation guidelines. The figure rises to 4.5 million on high-release days.
Nature Food · Trinity College Dublin · 2020Are glass baby bottles better than plastic? Yes. Glass baby bottles do not release microplastics, do not contain bisphenols, and do not leach chemicals when heated. A 2020 study from Trinity College Dublin found that standard polypropylene bottles release up to one million microplastic particles per day into formula under normal preparation guidelines.
The best glass baby bottles use borosilicate glass, which is more durable and heat-resistant than standard glass. Our top picks are Pura Kiki, Dr. Brown's Natural Flow Glass, Philips Avent Natural Glass, and NUK First Choice Glass.
The short answer is yes, on the available evidence. Glass releases no microplastics from the bottle body, contains no bisphenols, and doesn't interact chemically with hot liquid. The 2020 Trinity College Dublin study found that polypropylene bottles, prepared according to WHO sterilisation guidelines, can release up to one million microplastic particles a day into the formula inside them.
Polypropylene plastic makes up the vast majority of baby bottles sold globally. It is cheap, lightweight, and shatterproof. It is also, when heated, a significant source of microplastic exposure for infants. Understanding why heat matters and which materials sidestep the problem entirely is what this page is about.
Microplastics are shed from bottle surfaces as a result of a chemical interaction between the plastic polymer and water , and the process accelerates dramatically with temperature. Sterilising a polypropylene bottle in boiling water releases more microplastics than any other single step in formula preparation. Adding hot water to mix formula is the second largest source. The WHO's own recommended preparation method , using water above 70°C to kill bacteria , is, in a polypropylene bottle, simultaneously the method most likely to maximise microplastic exposure.
On baby bottles specifically, the regulatory picture is more nuanced than the formula story. Here is what each jurisdiction actually does , and where the real difference lies.
When BPA was banned from baby bottles, manufacturers didn't remove the chemistry , they replaced it. BPS (bisphenol S) and BPF (bisphenol F) stepped in. They are structurally similar to BPA. Early research suggests similar endocrine-disrupting properties. In the US, they are not banned at a federal level. A bottle labelled "BPA-free" in an American store may simply be a BPS or BPF bottle. The label tells you what was removed. It tells you nothing about what replaced it.
The EU's 2025 regulation closed this loophole by banning the entire bisphenol family. The US has taken no equivalent federal action. This is why "BPA-free" is a marketing term. "Bisphenol-free" is a standard. Borosilicate glass contains neither , and sidesteps the question entirely.
"The bottle is glass. The teat is silicone. The collar is polypropylene. No baby bottle is made of one material, and that's worth knowing before you choose."organicnewborn.com
Four materials show up in modern baby bottles, with very different safety profiles. Below: what each one is, what the research currently says, and how each one performs against the others under conditions of normal use.
Polypropylene is the standard material for most baby bottles sold worldwide. It is lightweight, transparent, and shatterproof , which is exactly why it became dominant. The problem is what happens when it meets heat.
During sterilisation in boiling water, polypropylene surfaces undergo a thermal-oxidative process that causes microscopic particles to flake from the bottle's inner surface directly into the liquid. Shaking the bottle to mix formula accelerates this further. The particles are too small to see, too small to taste, and their long-term health consequences are not yet fully understood. What is known is that they are entering your baby's body in significant quantities at every single feed.
A 2020 study in Nature Food by Trinity College Dublin tested ten polypropylene bottles using WHO-recommended preparation guidelines. Polypropylene bottles released up to 16.2 million microplastic particles per litre. Based on feeding data from 48 regions, researchers estimated infant exposure of between 14,600 and 4.55 million particles per day. Sterilisation in boiling water was identified as the highest single source of particle release. A subsequent study found that the particles trigger intestinal inflammation in human cell models via an oxidative stress pathway.
The data is clear enough that we don't recommend polypropylene as a primary bottle material. If you already own polypropylene bottles, prepare formula in a glass vessel first, let it cool before transferring, and never microwave. But if you're choosing from scratch, glass is the more defensible starting point , by a significant margin.
Silicone appears in baby products in two ways: as the teat material on almost every bottle , including glass ones , and as the body material for soft, squeezable silicone bottles like Comotomo.
Silicone is genuinely better than polypropylene. It doesn't contain bisphenols, and in most formulations it is chemically stable. The complication is that silicone is not particle-free. Research shows that steam sterilisation of silicone components generates particles , silicone-based rather than conventional microplastics, and less studied in terms of long-term implications. The honest answer is that silicone is a meaningful step up from polypropylene, but it is not the same as glass.
A 2024 study in Science of the Total Environment found that silicone feeding bottles release between 1,465 and 5,893 particles per litre under typical usage conditions , significantly lower than polypropylene, but measurable. A separate study found that steam disinfection of silicone pacifiers generated approximately 0.66 million particles annually. The predominant particles released were polyethylene-based rather than silicone itself, suggesting other polymers are present as processing additives in the silicone compound.
For teats, silicone is the standard and there is no realistic alternative. For bottle bodies, we prefer borosilicate glass. Silicone bottles like Comotomo have real advantages , softness, ease of transition from breast , and are meaningfully safer than polypropylene. But they are not the same as glass, and we think parents deserve to know that clearly.
PPSU (polyphenylene sulfone) and Tritan copolyester are premium plastics marketed as safer alternatives. They are bisphenol-free and significantly more heat-resistant than standard polypropylene , meaning they shed fewer microplastics at typical use temperatures.
They are genuinely better than polypropylene. Brands like Hegen use PPSU. The honest limitation: fewer microplastics is still not zero, and they remain plastic. For families who need an unbreakable bottle , for travel, nursery, or a baby who drops things , PPSU is our preferred plastic. But it is a pragmatic compromise, not a solution.
PPSU feeding bottles were included in the 2024 Science of the Total Environment study. Under typical usage, PPSU bottles released a median of approximately 1,500–2,000 particles per litre , significantly lower than polypropylene but measurable. Notably, the predominant particles released were polyethylene rather than PPSU itself, suggesting contamination from manufacturing processes or added components. This remains an active area of research with limited long-term data.
If you need a lightweight or unbreakable option, PPSU is the plastic we'd choose. Avoid heating formula directly in it where possible. It is a considered middle-ground , better than most of what's on the market, but not the same as glass. Prepare formula in a non-plastic vessel and transfer when cooled to reduce exposure further.
Borosilicate glass is the only bottle body material that releases zero microplastics. It contains no bisphenols, no polymer chains to degrade, and has no chemical interaction with hot liquids. It is the material that sidesteps every question this page raises , and it is the starting point for every recommendation we make.
The tradeoff is weight and breakability. Glass bottles are heavier and will shatter if dropped on a hard floor without a sleeve. Most parents who use glass bottles use a silicone sleeve for grip and protection, which reduces breakage risk considerably.
One important note: not all glass bottles use borosilicate. Standard soda-lime glass is more prone to thermal shock , cracking when hot liquid meets a cold bottle. Look for "borosilicate" explicitly in the product specifications before buying.
Glass bottles were included as a baseline in the Trinity College Dublin Nature Food study. The study confirmed that glass bottles release no detectable microplastics from the bottle body under standard preparation conditions. Borosilicate glass is chemically inert across the temperature range used in formula preparation and sterilisation, and contains no bisphenols or polymer additives. It is the only material in this comparison for which the research raises no ongoing questions about particle release from the bottle body itself.
Glass is our starting recommendation for all newborns. The weight concern is real but manageable , a silicone sleeve solves it. The teat is silicone like every other bottle, and the collar is polypropylene , but the body, the part that holds the milk, is fully inert. For a baby drinking eight to twelve feeds a day in the first months of life, that difference compounds.
A glass bottle is not one material. Here is what every component is made from , and what to know about each one.
The body holds the milk and is the part this whole decision is about. In a glass bottle, this is entirely inert , no microplastics, no bisphenols, thermally stable. Confirm the bottle specifies borosilicate rather than standard soda-lime glass.
Every bottle teat is silicone , there is no realistic alternative. Silicone releases fewer particles than polypropylene and contains no bisphenols. It is the remaining variable in an otherwise inert system. Replace teats regularly, as wear increases particle release. Avoid latex teats (allergy risk, less stable over time).
The collar that screws the teat onto the bottle is almost universally polypropylene. It does not come into direct contact with the milk under normal use , so its microplastic contribution is low. Some brands (Pura Kiki) offer stainless steel collars as an option, reducing plastic component count further.
Anti-colic vent systems (Dr. Brown's internal vent, for example) are typically polypropylene or silicone components that run inside the bottle and do contact milk. Worth factoring in for a baby without colic , a non-vented glass bottle has fewer materials in contact with the feed.
A silicone sleeve wraps the outside of the glass bottle. It does not touch the milk. Its job is grip, temperature insulation, and breakage protection. We recommend using one , it significantly reduces the risk of drops and makes glass bottles easier to hold during night feeds.
Dust caps that cover the teat for transport are polypropylene but do not contact milk. Low concern. Dry thoroughly before capping after sterilisation to avoid moisture build-up inside the teat.
If switching to glass isn't possible right now, these steps , developed by the Trinity College Dublin research team , significantly reduce microplastic exposure from polypropylene bottles.
Mix formula in a glass jug, ceramic bowl, or stainless steel vessel. Never add hot water directly to the plastic bottle. This single step removes the largest source of microplastic release.
Once prepared, wait until the formula has cooled to room temperature before pouring into the bottle. Heat is the primary driver of particle release , cooling the formula first removes that trigger.
After sterilising in boiling water, rinse the bottle with cool, sterile water before filling. Sterilisation is the highest-release moment , this step flushes particles out before the feed.
Microwave heating creates uneven hot spots and dramatically elevates microplastic release. Warm formula by placing the bottle in a bowl of warm water for a few minutes instead.
Three questions. A recommendation that puts material safety first , with the honest tradeoffs laid out clearly.
Every pick we recommend is either borosilicate glass or our preferred plastic alternative. We list the plastic components on every card , because transparency is the whole point of this site.
Every bottle here is either borosilicate glass or our preferred plastic alternative. We list the plastic components on each card , because transparency about what you're buying is the whole point of this site.
Our top pick on material safety. Borosilicate glass body with an optional stainless steel collar , the only bottle on this page that lets you remove the polypropylene collar entirely. No internal vent system means the fewest materials in contact with milk of any bottle we recommend. Converts to a sippy cup and straw cup as the baby grows.
See where to buy →The strongest choice for colicky or gassy babies. The internal vent system channels air through the back of the bottle rather than through the milk, clinically shown to reduce colic, spit-up, and gas. Glass body with vent components in polypropylene and silicone inside , more parts to clean, but worth it for a colicky baby.
See where to buy →The strongest choice for families switching between breast and bottle. The Natural teat is shaped to encourage the same latch as breastfeeding, reducing nipple confusion. Borosilicate glass body, wide neck for easy cleaning, and a silicone sleeve included in the box. Widely available and well made.
See where to buy →NUK's orthodontist-designed teat is shaped to mimic the natural stretch during breastfeeding , a strong choice for combination feeding families. German-made borosilicate glass with a broad range of teat sizes to grow with the baby. Solid engineering, clean design, widely available across Europe.
See where to buy →If you need an unbreakable bottle , for travel, nursery, or older babies who drop things , Hegen PPSU is our preferred plastic option. Bisphenol-free and significantly more heat-stable than polypropylene. Prepare formula in a non-plastic vessel and transfer when cooled to minimise exposure. Not glass, but the most considered plastic choice we have found.
See where to buy →For babies who resist accepting a bottle after breastfeeding, Comotomo's soft silicone body can ease the transition. Bisphenol-free and safer than polypropylene , but as a fully silicone bottle it ranks below glass options on pure material safety. A pragmatic choice for the transition phase, not a long-term material recommendation.
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