Sign up for a doorstep milk delivery in returnable glass if one exists locally, or buy the largest HDPE bottle you can use before it spoils instead of several small ones.
A 2 litre HDPE milk bottle weighs around 40 g; a household using two a week is about 4 kg of plastic a year, avoided entirely with returnable glass. A 2025 life-cycle assessment (LCA) of reusable glass wine bottles found break-even depends on trip distance and the number of wash cycles.
The catch: a 1 pint glass milk bottle weighs around 200 to 250 g, roughly ten times a plastic bottle holding the same milk. Melting glass takes furnaces at about 1,500 degrees Celsius, and the extra weight costs fuel at every step, so per single use glass is worse than plastic on greenhouse gas (GHG), energy and water (National Association for PET Container Resources (NAPCOR), the PET industry body, 2023). Recycling the glass saves only a little of that energy, so a glass bottle you recycle rather than return is not an improvement. Returnable glass wins because that upfront cost is spread over many refills, as long as bottles come back often and travel short distances.