Counting carbon in a shoe, a quick worksheet for stitching and reinforcement hotspots

Shoes look small.
Carbon numbers can feel big.
Good news: you can count the main bits with a short worksheet and fix the hotspots fast—especially around stitching and reinforcements.
Plain steps below. Use one style this week.

What you need (nothing fancy)

• A kitchen scale (grams).
• Your BOM (bill of materials).
• A ruler and a piece of string (to measure seam length).
• Emission factors (EFs) from suppliers or trusted databases: in kg CO₂e per kg for materials, and kg CO₂e per km for thread. If you don’t have exact numbers, start with industry averages and replace later.

The five-part worksheet (one page)

1) Map the shoe like a pizza
Slice into: upper fabric, thread, seam tape/film or glue, reinforcements (toe puff, counter, eye-stay, rand), lining/foam near seams, and transport (optional starter). Write each slice in a column.

2) Weigh or estimate

• Upper offcuts hard? Then measure by area: weigh a 10×10 cm swatch and scale up.
• Thread length: run a string along all seams of one shoe; add 15% for bartacks and waste.
• Films/tapes: measure width × length × thickness × density, or weigh a sample strip and scale.

3) Pick emission factors (EFs)

• Use supplier-specific EF if you have it (best).
• If not, use an LCA database average (okay).
• Note the source and year next to each EF. Numbers without notes get messy later.

4) Do the tiny math

• Materials: mass (kg) × EF (kg CO₂e/kg) = kg CO₂e

• Thread: length (km) × EF (kg CO₂e/km) = kg CO₂e

• Transport (optional): ton-km × EF (ask logistics).

5) Color the hotspots
Mark the two biggest boxes red. These are your first levers for improvement next season.

Quick example (one shoe, simple numbers)

• Upper knit (polyester): 120 g → 0.12 kg × EF 3.0 = 0.36 kg CO₂e

• Thread (rPET): 85 m → 0.085 km × EF 0.9 = 0.0765 kg CO₂e

• Seam tape (PET): 6 g → 0.006 kg × EF 2.5 = 0.015 kg CO₂e

• Toe puff (rPET nonwoven): 5 g → 0.005 kg × EF 2.2 = 0.011 kg CO₂e

• Counter (bio-nylon): 12 g → 0.012 kg × EF 4.2 = 0.0504 kg CO₂e

• Adhesive (water-based): 4 g → 0.004 kg × EF 1.8 = 0.0072 kg CO₂e
  

This mockup says: upper fabric dominates, but counter and thread + stitch choices are not tiny. When multiplied by pairs, they matter.

Stitching levers (fast wins)

Stitch density (SPI).
When the number of stitches increases, more thread is needed, which causes more needle holes and may lead to more tape.

• If the project permits, a shift from 11 SPI to 9–10 SPI on wovens, or 12 to 10–11 on knits. Test strength first. Keeping performance while dropping 8–12% thread length is common.

Ticket size.
Use the finest thread that still passes the pull and slippage. Smaller ticket = smaller holes = less thread mass = lower EF × length.

Material family.
Match sewing machine thread polymer to upper polymer (e.g., polyester sewing thread with PET fabric). It won’t lower your per-pair number by itself, but it enables recycling, which avoids future virgin emissions—your hangtag story and end-of-life math both get better.

Anti-wick finishes (metal-free).
A dry seam survives longer → fewer warranty returns → hidden carbon saved. Durability is climate math.

Reinforcement levers (shape without weight)

Toe puff / counter choice.

• Swap virgin sheets for recycled-PET nonwovens or bio-based nylon that heat-form fast.
• Try lattice or zoned thickness: material only where the force lives. Cutting 20–30% mass here is common with the same fit.

Bonding method.

• Prefer heat-activated films from the same polymer family; avoid thick, solvent glues. Films use less mass and help clean recycling streams.

Edge geometry.

• Round corners (≥6–8 mm) and feather edges so you need less tape and avoid rework. Rework is hidden carbon.

Add these two checks to your worksheet

1. A) Flex life vs. carbon
   After your first pass, run 50k flex on a sample pair. If a lighter seam fails early, the carbon “saved” is fake—you’ll rebuild or replace. Only log savings for specs that pass durability.
2. B) Wet wick strip
   Dip a stitched coupon 10 mm into dyed water for 30 min. If the wick climbs high, you’ll add tape later (more mass). Fix the seam now (needle size, anti-wick thread, tension), then lock the lower-mass bill.

“Swap table” for next season (put this under your worksheet)

One-week pilot plan

1. Pick one hero style.
2. Fill the worksheet with current numbers (fabric, thread, tape, puffs, counter).
3. Prototype two light-touch changes: (a) drop SPI by 1 on non-stress seams, (b) switch counter to zoned or lighter sheet.
4. Re-measure grams and re-compute CO₂e.
5. Run pull, slippage, 50k flex, and wick tests.
6. If pass, lock the spec and scale next colorway. If not, revert one step and try a finer thread + small bar-tack instead of blanket high SPI.

Notes to print on the tech pack (save future time)

• “Mono-material upper: PET fabric + rPET thread + PET film.”
• “SPI: 10 on quarters, 11 on eyestay, 9 top-stitch (validate).”
• “Counter: bio-nylon zoned; cool-clamp 2 s.”
• “Record seam length per size for thread EF update.”

Wrap (small and true)

Counting carbon in a shoe is not magic.
It is grams times factors—then smart swaps on seams and reinforcements.
Lower SPI is safe. Choose lighter, smarter counters. Match polymers. Keep seams dry and durable.
Do the worksheet once, improve twice, and your pair steps out with less footprint and the same good ride.