Sustainability5 min read

Recyclers sort by material and by density. A closure that mixes polymers, carries a metal liner, or floats when the bottle sinks stops being a resource and becomes a contaminant — often for the whole bale, not just for itself.

One material, wherever you can

A polypropylene closure on a polypropylene bottle is the simplest case. Where the bottle is PET, a PP or PE closure still separates cleanly in a float-sink step, because it floats while PET sinks. Metal liners and mixed inserts break that separation and are worth designing out early.

Lightweighting has a floor

Removing material lowers impact, but only until sealing force or drop performance suffers. The useful target is the lightest part that still passes the same leak and transit tests as the part it replaces — not the lightest part that can be moulded.

Keep the closure on the bottle

Tethered designs keep the closure with the pack through collection, which raises recovery rates and reduces litter. They also change the opening motion, so they need testing with real users rather than only an engineering sign-off.

Colour is a sorting decision

Dark pigments can defeat near-infrared sorting, which means a technically recyclable closure gets rejected at the plant. If a closure has to be dark, specify a detectable pigment system and confirm it with a recycler rather than assuming it will pass.