A formula can be flawless in the lab and fail in the packaging. A cream that loses its scent, a serum that changes color, or a bottle that deforms after a few weeks: often the problem lies not in the formula or the packaging separately, but in how they interact.
Choosing the right material from the start saves repeated testing, returns, and supplier changes midway through the launch. In this guide, we review what can go wrong, how the most common plastics behave, and which material is suitable depending on the type of product.
What can happen when the packaging and formula are not compatible
The interaction between the packaging and the product can go in both directions:
- Absorption: plastic absorbs part of the formula, especially perfumes and essential oils. The product loses aroma or concentration of active ingredients.
- Permeation: some components pass through the wall of the container. Water or perfume escapes, or oxygen enters and oxidizes the formula.
- Migration: substances from the material (additives, manufacturing residues) transfer to the product.
- Tensile cracking: certain surfactants and oils, combined with the tension of the container itself (at the thread or when tightening the cap), can cause cracks.
- Deformation: the container sinks or bulges because it loses or gains volume.
Therefore, Regulation (EC) No. 1223/2009 on cosmetic products requires that the safety report includes information about the packaging material. The packaging is part of the product; it is not just a simple container.
The most common plastics in cosmetics
| Material | Strengths | To take into account |
| PET | Transparent, rigid, and with good oxygen barrier. Very versatile | Does not allow hot filling. With very concentrated essential oils, it's better to conduct tests. |
| PETG | Glass-like transparency, good impact resistance | Chemical resistance slightly lower than that of PET against some solvents. Consult the manufacturer's data sheet. |
| PP | Good chemical and heat resistance. Commonly used in jars, caps, and pumps. | Translucent, not transparent. Moderate oxygen barrier |
| HDPE | Very good chemical resistance. Opaque or translucent, economical | More permeable to perfumes, essential oils, and oxygen. Can absorb aroma |
| LDPE | Flexible: ideal for squeeze bottles and tubes | It is the most permeable of the five. More sensitive to cracking with concentrated surfactants. |
| Glass (alternative) | Inert and with total barrier. In amber, it protects from light | Heavier and more fragile. Higher transportation cost |
If you want to delve into the differences between these materials, read our article [What is the difference between laboratory plastics: PP, HDPE, PET].
What material to choose according to the formula
This table is for guidance. The actual compatibility depends on the concentration of each ingredient, the thickness of the packaging, and the storage conditions.
| Product type | Common options | Warning |
| Aqueous formulas (toners, micellar waters, gels) | PET, PP, HDPE | Few incompatibilities. Pay attention to the closure |
| Emulsions (creams, lotions) | PP, PET, HDPE jars, airless containers | If they contain sensitive actives, it's better to use airless or opaque. |
| Vegetable oils and oily serums | PET, glass | HDPE and LDPE can absorb some of the oil and perfume |
| Pure or highly concentrated essential oils | Glass, preferably amber | Avoid polystyrene (PS) and, in general, test with any plastic |
| Products with a lot of alcohol (perfumes, colognes) | Glass | In plastic, they can lose aroma due to permeation |
| Hand sanitizers | HDPE, PET | Check that the pump and the cap are compatible with alcohol |
| Light or oxygen-sensitive actives (vitamin C, retinol) | Opaque airless, amber glass | Avoid transparent containers and those that allow air to enter with each use |
| Shampoos and shower gels (surfactants) | HDPE, PET, PP | With concentrated surfactants, monitor for cracking, especially in LDPE |
Don't forget the closing
Many incompatibilities do not appear in the bottle, but in the cap, the pump, or the dropper: seals that swell, metal springs in contact with the formula, or rubber pipettes that degrade with essential oils. Each component can be made of a different material, so all of them need to be checked, not just the body of the container.
For thread sizes and types, consult our guide [Most Common Thread Types in Containers: DIN18, PP28, and GL45].
Recycled plastics: one more point to verify
More and more brands are using recycled plastic (PCR) for sustainability reasons. It is a good option, but its properties can vary between batches and compared to virgin material. If you switch to PCR, repeat the compatibility tests even if the formula is the same. We discuss these trends in [Trends in Sustainable Cosmetic Packaging from 2026].
How to check compatibility
No table replaces a test with your actual formula:
- Request samples of the complete packaging: body, closure, and accessories.
- Conduct stability and compatibility tests with the packaged product at room temperature and under accelerated conditions (more heat, light), according to the protocol of your laboratory or your safety evaluator.
- Check periodically: weight (product loss), color, smell, appearance of the packaging, and functionality of the closure.
- Document the results: they will be useful for the product file and if you change the reference in the future.
Frequently Asked Questions
Does PET work for essential oils?
For formulas with diluted essential oils, it usually works well. For pure or highly concentrated essential oils, the safest option is amber glass. In any case, it's advisable to conduct tests.
Why does my cream lose its scent in the container?
Probably the material absorbs the perfume or allows it to escape through the wall. This happens more with HDPE and LDPE. A material with a better barrier, like PET, or a glass container can solve this.
What packaging is best for a vitamin C serum?
A container that protects from light and air: an opaque airless bottle or an amber glass bottle with a dropper, if the formula allows it.
Can I change the container without repeating the tests?
It is not advisable. A change in material, supplier, or from virgin plastic to recycled plastic can alter compatibility, even if the packaging looks identical.
Conclusion
The packaging is part of the product. Choosing it based on the formula, and not just its appearance or price, prevents stability issues and protects the end customer's experience. When in doubt, always test with the actual formula and review all components, including the closure.
Do you have a formula and don't know which container to choose? Tell us what it contains and we will help you find the most suitable options from our catalog.
View the catalog of cosmetic packaging