Interpreting Clo
Translating a clo number into the shirts, layers, and jackets on your shelf.
Clo is the target; building the layer stack is the implementation — and the stack order matters.
The calculator tells you to hit 2.5 clo. The closet has a fleece and a down jacket and a shell. Which combination delivers 2.5 clo, and in what order? The three-layer model — base, mid, shell — is the industrial-strength answer, and the order matters for moisture management.
Quick answer
Clo is the target; building the layer stack is the implementation — and the stack order matters.
Key points
- ▸ Base layer: moisture wicking, typically 0.1-0.3 clo. Merino or technical synthetic. Never cotton in cold — cotton soaks and chills.
- ▸ Mid layer: insulation. Fleece (0.3-0.5 clo), down sweater (0.5-0.8 clo), synthetic puffer (0.4-0.7 clo).
- ▸ Outer shell: wind and water stopping. Near-zero clo but blocks convective loss, which can multiply effective insulation of lower layers by 30-50%.
- ▸ Vapor movement: sweat has to escape the base outward. A waterproof shell that does not breathe creates a sauna and soaks the insulation.
- ▸ Target stack depth: sum clo values of all layers, multiplied by 0.8 for overlap losses. Aim 20% above required clo for buffer.
Examples
- Target 1.5 clo · 35°F walkingMerino base (0.2) + fleece (0.4) + light shell (0.1) + pants/hat (buffer). Total ~0.7 layered × coverage factor ≈ 1.5 clo. Enough.
- Target 3.0 clo · 10°F standingHeavyweight merino (0.3) + down mid (0.7) + heavy insulated parka (1.5) + bibs + thick hat + gloves. Active insulation + wind blocking.
- Target 4.5 clo · expeditionBase + mid + heavy insulation + shell + oversized parka + expedition mittens. Redundant layers around core; extremities often the bottleneck.
When to use which tool
- Insulation Logic · Clo UnitsBefore dressing — match the calculated target clo to a layer stack, allow buffer for longer stops.Required clothing insulation in clo units for air temperature and activity level. Suggested garment stack.
- Kinetic Expenditure · METActivity level changes required clo. A stop-go outing needs a flexible stack.Calories burned per activity using the MET (Metabolic Equivalent of Task) method from the Compendium of Physical Activities.
Related
- Insulation Logic · Clo UnitsRequired clothing insulation in clo units for air temperature and activity level. Suggested garment stack.
- Kinetic Expenditure · METCalories burned per activity using the MET (Metabolic Equivalent of Task) method from the Compendium of Physical Activities.
- The Clo Insulation UnitHow engineers quantify "enough clothing for this temperature".
- Clo Formula Edge CasesWhen the simple formula under-states required insulation — sometimes badly.
- Interpreting Calorie BurnWhy 300 kcal in a workout does not equal 300 kcal of fat loss.
Frequently asked questions
› Is down or synthetic better? Comparison
Down has higher clo per gram but collapses when wet. Synthetic retains ~70% insulation wet. For wet-cold conditions (rain, snow, sweating), synthetic. For dry-cold (alpine, arctic), down wins on weight.
› Do heated jackets work?
Yes — they add active heat rather than passive insulation. Think of them as +0.5-1.0 effective clo while powered. Great for stop-go activity; battery life is the limit.
› How should I use this guide with a Kefiw tool? How-to
Use the guide as the plan and the linked Kefiw tool as the check. Read the steps first, try the move manually, then use the tool to compare outputs, catch edge cases, and decide whether the result actually fits your task.
› What mistake do tool guides help avoid? Troubleshooting
Tool guides help avoid using a utility mechanically without understanding what you are trying to accomplish. Most word, writing, and text utilities are fast, but speed can hide context mistakes. Know whether you are solving a puzzle, cleaning copy, drafting a line, or checking a rule.
› Can a tool guide help me learn the skill? How-to
A tool guide can help you learn if you pause before accepting the output and ask why it worked. Compare your first guess with the tool result, look for the rule or pattern, and repeat that review. Passive copying solves one task; active review builds the skill.