{"id":3559,"date":"2026-10-15T12:19:42","date_gmt":"2026-10-15T04:19:42","guid":{"rendered":"http:\/\/www.ars-infosys.com\/blog\/?p=3559"},"modified":"2026-10-15T12:19:42","modified_gmt":"2026-10-15T04:19:42","slug":"what-is-the-resistance-of-foil-lidding-to-chemicals-444a-e2b6cd","status":"publish","type":"post","link":"http:\/\/www.ars-infosys.com\/blog\/2026\/10\/15\/what-is-the-resistance-of-foil-lidding-to-chemicals-444a-e2b6cd\/","title":{"rendered":"What is the resistance of foil lidding to chemicals?"},"content":{"rendered":"

If you\u2019ve ever stood in a pharmaceutical packaging cleanroom, a food processing warehouse, or a diagnostic lab, you\u2019ve probably handled foil lidding without even realizing it. As someone who\u2019s spent 12 years running a foil lidding supply operation, I\u2019ve sat through countless client meetings where the first question isn\u2019t about cost or lead time\u2014it\u2019s about chemical resistance. It\u2019s the make-or-break detail that keeps a vaccine vial sterile, a packet of freeze-dried soup fresh, or a diagnostic strip from giving a false test result. Too many suppliers oversimplify this: they\u2019ll say \u201cfoil is chemical resistant\u201d like it\u2019s a one-size-fits-all trait, but anyone who\u2019s worked with packaging knows that\u2019s not true. Let\u2019s break down what foil lidding\u2019s chemical resistance actually means, how it\u2019s tested, and what you need to know before picking a material for your specific application. Foil Lidding<\/a><\/p>\n

<\/p>\n

First, start with what foil lidding is made of. The core isn\u2019t just plain aluminum\u2014our standard industrial foil is 99.9% aluminum, milled to a thickness between 0.05 mm and 0.2 mm, with a variety of coatings and laminates on either side that are non-negotiable for chemical resistance. The inner side (the part that seals to the container, whether that\u2019s a glass vial, plastic tray, or blister pack) needs to bond securely, so it\u2019s usually coated in a heat-sealable polymer. The outer side, which faces the outside environment, gets a protective layer to block moisture, UV light, and, most importantly, chemicals that could degrade the foil or seep through to the product.<\/p>\n

Let\u2019s get into the science of that resistance. Aluminum itself is naturally corrosion-resistant because it forms a thin, tightly bonded oxide layer when exposed to air. That layer is about 2 to 3 nanometers thick, and it works great for neutral chemicals like water, salt solutions, or mild sugars. But here\u2019s the catch: it breaks down when it interacts with strong acids (pH less than 4) or strong bases (pH higher than 9). If you put plain aluminum foil in battery acid or bleach, that oxide layer dissolves, and the foil starts to corrode within hours. That\u2019s why plain aluminum is never used as primary packaging for products with extreme pH levels\u2014you need extra layers to protect it.<\/p>\n

That\u2019s where the coatings come in. The most common outer coating for our foil lidding is a polyester (PET) layer, about 10 to 25 micrometers thick. PET is an extremely chemically stable polymer; it resists most acids, bases, alcohols, and common organic solvents like acetone, ether, and even mild hydrocarbons. For example, in the food industry, foil lidding with a PET outer layer is used to seal trays of marinara sauce (pH ~3.5, a mild acid) or salad dressings with vinegar, and it holds up for years without any degradation. In pharmaceuticals, it works for blister packs that hold solid tablets, since most excipients in tablets are neutral or slightly acidic.<\/p>\n

But PET isn\u2019t perfect. It\u2019s permeable to some organic solvents, especially at elevated temperatures. If you\u2019re packaging a product that uses strong hydrocarbons like gasoline, kerosene, or concentrated ethanol, PET won\u2019t stop those chemicals from seeping through. For those applications, we use polyvinylidene chloride (PVDC) as an outer coating. PVDC is a dense, non-porous polymer that\u2019s almost impenetrable to organic solvents. It\u2019s the same material used in Saran wrap, and it\u2019s been a staple in pharmaceutical and chemical packaging for decades because it resists even strong solvents. We once worked with a industrial chemical lab that needed lidding for small bottles of concentrated isopropyl alcohol (70% to 99% IPA) for lab equipment cleaning. They tried PET lidding first, and within three months, the lidding had blistered and developed pinholes where IPA had seeped through. Switched to PVDC-coated foil, and they\u2019ve had zero issues in five years.<\/p>\n

Then there\u2019s the inner seal coating, which is even more critical because it\u2019s in direct contact with the product. The inner coating has two jobs: it has to stick to the container, and it has to resist whatever is inside the container without leaching chemicals back into the product. The most common inner coatings are polyolefins, like polyethylene (PE) or polypropylene (PP). Low-density PE (LDPE) works for most neutral and mildly acidic products, but high-density PE (HDPE) or cast polypropylene (CPP) is better for higher temperatures or stronger chemicals. For example, if you\u2019re packaging a blister of suppositories, which are made of cocoa butter and mild active ingredients, LDPE works fine. But if you\u2019re sealing a tray of liquid fertilizer for hydroponics, which has a pH of 10.5 (a strong base), CPP is the way to go\u2014LDPE would start to soften and lose its seal within a few months, while CPP stays intact for up to two years.<\/p>\n

There are also more specialized coatings for extreme applications. For aerospace, where packaging has to survive exposure to jet fuel and high-altitude UV radiation, we use a polyimide (PI) outer coating. PI can resist temperatures up to 260\u00b0C and is almost completely impermeable to hydrocarbons, making it the only foil lidding that works for aerospace fuel component packaging. For medical diagnostics, where lidding might come into contact with blood or other biological fluids, we use a ethylene vinyl alcohol (EVOH) coating that resists enzymes, proteins, and even strong disinfectants like hydrogen peroxide.<\/p>\n

Of course, chemical resistance isn\u2019t just about the foil\u2019s material\u2014it\u2019s also about testing. As a supplier, we don\u2019t just guess if a foil will work for a client; we run standardized tests to verify it. The most common test is the ASTM D3070 standard for resistance of thin sheeting to chemicals, which involves submerging a sample of lidding in the target chemical for a set period of time (usually 24 to 720 hours, depending on the application) and then checking for changes in weight, thickness, tensile strength, and appearance. For pharmaceutical applications, we also test for extractables and leachables (E&L) per USP <661> guidelines, to make sure no harmful chemicals from the lidding migrate into the product. For food packaging, we test per FDA 21 CFR regulations to confirm compliance with food contact standards.<\/p>\n

I learned the importance of proper testing the hard way, early in my career. We had a client who made natural cleaning products, including a bottle of concentrated citrus cleaner that had a pH of 4.2. They ordered a standard PET-coated foil lidding, thinking it would work because PET resists acids. But after two months, they reached out saying the lidding had developed white corrosion spots, and some seal areas had broken. We ran a test and found that citrus cleaners have d-limonene, an organic compound in orange peel, that breaks down PET over time. The PET absorbed the d-limonene, which caused it to swell and lose its barrier properties. We replaced their lidding with a PVDC-coated foil, which doesn\u2019t absorb d-limonene, and that client has been with us for 10 years now. That mistake taught me that chemical resistance isn\u2019t just about pH\u2014it\u2019s about the specific chemicals in the product, even in small amounts.<\/p>\n

Another common misconception is that foil lidding is only for barrier purposes, but its chemical resistance also depends on how it\u2019s sealed to the container. A bad seal can let chemicals seep in even if the lidding itself is resistant. For example, if you heat-seal a foil lidding to a plastic tray at too low a temperature, the inner coating won\u2019t melt fully, creating gaps where chemicals can get in. If you use too high a temperature, you might burn the coating, creating weak spots. We work closely with our clients to optimize seal parameters, and we also offer compression testing to make sure the seal is strong enough to resist the pressure from inside the container (like from carbonated drinks, for example, which have higher internal pressure that can push chemicals through weak seals).<\/p>\n

What about common chemicals that people ask about most? Let\u2019s break down the ones we get asked about daily:<\/p>\n