Glass Containers and Packaging Glass

Soda-lime glass – the standard material for most packaging glasses – consists mainly of quartz sand (SiO₂), soda (Na₂O), and lime (CaO). This composition makes it economical, easily formable, and versatile – for example, for beverage bottles, canning jars, yogurt jars, or household storage containers.

It is taste-neutral, food-safe, and offers high transparency. However, it has limited resistance to temperature changes and is less chemically resistant than special glasses – an important factor for sterile goods or aggressive contents.

Manufacturing process of soda-lime glass for glass containers:

Soda-lime glass can be efficiently melted and formed at comparatively low temperatures (approx. 1,400 °C) – ideal for mass production. The melt is continuously degassed and homogenized before being divided into drops and blown or pressed into molds.
To minimize stress, cooling takes place in precisely controlled cooling lines. Depending on the application, the glass can also be coated or colored.

Soda-lime glass is the robust, reliable all-rounder among packaging glasses – ideal for standardized products with moderate chemical and thermal stress.

Borosilicate glass is a chemically particularly resistant glass that remains dimensionally stable even at high temperatures and sudden temperature changes. It consists of an increased proportion of silicon dioxide (SiO₂) and boric acid anhydride (B₂O₃) and is used in the field of glass containers primarily where sensitive or aggressive filling materials need to be packaged safely and permanently – for example, in the pharmaceutical industry, in laboratories, or for heat-resistant food storage containers.

Typical applications include medicine vials, ampoules, syringe bodies, test tubes, but also heat-resistant canning jars or special packaging for sensitive cosmetics. The glass is taste-neutral, inert, sterilizable, and resistant to chemicals and thermal stress.

Compared to borosilicate glass for technical applications, the composition in the container glass sector is slightly adjusted: the boron content is somewhat lower to allow for better formability in industrial production lines. Compared to tableware borosilicate, the focus is more on sterilizability, break resistance during transport, and mass processability – less on optical brilliance or design.

Manufacturing process of borosilicate glass for glass containers:

Production takes place at high temperatures (up to 1,600 °C) in melting furnaces designed for the tough, difficult-to-form borosilicate mass. The material is usually processed using tube glass methods, press-blow techniques, or segmented molds for small volume containers. The goal is to produce a high-purity, low-stress glass mass with the lowest possible thermal expansion – important for applications where containers must be autoclaved, sterilized, or heated.

Opal glass – also known as milk glass – combines functional light protection with a high-quality, brand-defining appearance. It is primarily used in the cosmetics, food, and pharmaceutical industries when light-sensitive products such as creams, syrup, or milk need to be simultaneously protected and attractively packaged.

Typical applications include cream jars, medicine vials, perfume bottles, or milk bottles. The translucent, usually white glossy surface protects the content from UV radiation and gives the product a noble, recognizable appearance.

Difference from opal glass in tableware:

In contrast to opal glass in the kitchen area, which is designed for thermal stress (e.g., dishwasher, oven) and mechanical robustness, the focus in the container sector is clearly on light protection, thin-walledness, and decorative design possibilities. The formulation is therefore balanced differently – in favor of formability and design, less for everyday heat exposure.

Special features in the manufacturing process of opal glass as container glass:

The typical opacity is created by adding opacifying agents such as fluorides or phosphates. During controlled cooling, these form microfine crystals that scatter light and create the characteristic milk glass effect. For a uniform, color-stable surface, precise temperature control throughout the entire melting and cooling process is essential. Even small deviations can impair optical quality. For brand presentation, opal glass is additionally refined with screen printing, embossing, metallic or color effects – often in combination with individual shapes for high recognition.