Chemical reaction and zip: what they have in common

Step 1. Chemical reaction — is used in — Airbag. The gas comes from an instant reaction of sodium azide.
Step 2. Airbag — is made of — Nylon. The airbag is nylon.
Step 3. Nylon — is material for — Backpack. Nylon.
Step 4. Backpack — has part — Zip. Zips.