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Melting versus mashing

Why Does Glass Recycle Better Than Paper?

Melting a material rebuilds it exactly, but tearing fibres apart shortens them a little every single time.

Melted back Glass and metal — asgood as newMashed back Paper — a littleshorter each time
How you undo it decides how often you can.

  1. Step 1 of 5

    Recycling only works if you can get back to the raw material.

    Collected Sorted bymaterial Returned to raw material Made intosomething newLoop

    It is not enough to collect a thing. There has to be a way to return it to the state it was in before it was made into anything.

  2. Step 2 of 5

    Melting forgets everything.

    1 An old can2 Melted down3 Atoms inexactly thesame state as

    Heat glass or aluminium until it flows and the atoms lose all memory of the shape they were in. What cools out is identical to material that never went round.

  3. Step 3 of 5

    Paper cannot be melted, only pulped.

    New fibrelong and strongThird time roundnoticeablyshorterSeventh timetoo short tohold together

    Fibres are torn apart mechanically, and a few break every time. Shorter fibres grip each other less well, so the paper gets weaker with each pass.

  4. Step 4 of 5

    Mixing materials is what breaks the loop.

    One material Easy — melt itBonded layers Card, plastic and foil,stuck as one

    A drinks carton is card, plastic film and aluminium bonded together. Each is recyclable alone, but separating them needs a special plant most places do not have.

  5. Step 5 of 5

    Aluminium is the one that really pays.

    From oreenormouselectricityFrom old cansabout 95% less

    Making aluminium from ore takes a huge amount of electricity. Melting old cans takes about a twentieth of it, which is why a used can is worth money.

    An aluminium can put in a recycling bin can be melted, rolled, filled and back on a shelf in about six weeks.

The short version

Materials that can be melted come back identical and recycle almost forever, while paper fibres shorten each time and eventually run out.

Try it yourself

Sort one day's rubbish into single materials and mixed ones. The mixed pile — crisp packets, coffee cups, blister packs — is the hard part of the problem.

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