Catharine’s question…Love the podcast, I especially like the beauty science or bullsh*t segment. (So do the guys in the family). Anyhow, my question may be more marketing than science. When I travel I prefer to buy products in plastic containers instead of glass because of the weight. This is often difficult to do with my favourite products. I have always assumed the reason for glass packaging was marketing – to give an aura of luxury and quality. Am I wrong? Is there some science reason for glass?
The Beauty Brains respond:
When to pay for a nice piece of glass
Plastic is a great packaging option because it’s cheap and lightweight. But there are at least three reasons that cosmetics should be packaged in glass instead of plastic:
1. To protect the product from outside elements
A key role of packaging is to protect the product from the elements, particularly oxygen, because oxygen molecules can slip through certain plastics. While oxygen transmission can be reduced through the use of multilayer plastics equipped with barrier coatings, glass is an almost perfect barrier. Therefore, for formulations which are very sensitive to oxygen (think antioxidants) glass may be a superior material. Keep in mind, however, that a squeezable plastic tube which doesn’t expose the product to air will do a better job of protecting it from oxygen than an open mouth glass jar that exposes the product to air and to your fingers every time you apply it.
Protecting the product from light is also an issue. A darkly tinted glass container may do a better job of protecting a product from fluorescent light than a thin-walled plastic tube.
2. To protect the package from the product
Some formulas can actually interact with plastics to compromise the integrity of the package. Perfumes are a classic example. Due to the solvent nature of the alcohol and the perfume oils themselves some perfumes can actually dissolve plastic containers. That’s why you almost universally see fragrances packaged in glass. Other formulas can cause plastic “crazing” which results in the appearance of small cracks in the package wall that weakens it. In either case such interactions can cause the package to rupture. Glass packages are impervious to this problem.
3. To protect the product from the package
Even if the integrity of the package itself isn’t compromised, the quality of the formula may be impacted by formula-plastic interaction. That’s because certain ingredients in the formula can leach plasticizers out of the package. These chemicals can interact with the formula and negatively affect its stability.
The Beauty Brains bottom line
There are some cases where glass is technically superior to plastic. But more often than not it’s used to connote high quality and therefore justify the price of more expensive products.