Aluminium foil layer and fitness tracker: what they have in common

1. Step 1. Aluminium foil layer — is part of — Tetra Pak. A barrier against light and oxygen.
2. Step 2. Tetra Pak — is made of — Polyethylene. Polyethylene.
3. Step 3. Polyethylene — is material for — Surgical mask. Non-woven polypropylene.
4. Step 4. Surgical mask — evolved into — Respirator. A filtering mask.
5. Step 5. Respirator — is made of — Vulcanized rubber. The mask is rubber.
6. Step 6. Vulcanized rubber — is material for — Fitness tracker. The strap is silicone.

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