Clothing Insulation Data
WhetherWear publishes two small reference tables: the insulation of leg coverings and of mid layers, in clo, drawn from ASHRAE 55 and ISO 9920. Values tabulated in those standards are marked as measured; values that are not are marked as estimates and shown with the two published neighbours they sit between. Nothing here is derived from opinion.
Leg coverings
Insulation of a single leg garment, in clo. The final column converts that into a whole-body comfort shift at rest, expressed as a range because the conversion is not a constant.
| Leg covering | clo | Provenance | Whole-body comfort shift |
|---|---|---|---|
| Bare legs | 0 | Measured | 0–0°F |
| Sheer tights (roughly 15–20 denier) | 0.02 | Measured | 0.2–0.3°F |
| Opaque tights (roughly 40–80 denier) | 0.1 | Estimated (between 0.02 and 0.15) | 0.9–1.3°F |
| Fleece-lined tights | 0.2 | Estimated (between 0.15 and 0.28) | 1.8–2.6°F |
| Thin trousers | 0.15 | Measured | 1.3–2°F |
| Thick trousers or lined jeans | 0.24 | Measured | 2.2–3.1°F |
The figure most people find surprising. A sheer tight is worth roughly a fifth of an opaque one and about an eighth of a thin trouser. It changes how bare legs look rather than how cold they are.
Mid layers, and their air permeability
Insulation again in clo, beside an ordinal for how readily air passes through the garment. The ordinal is deliberate: published permeability depends on fabric weight and construction, so a single decimal would be a precision the source data does not support.
| Layer | clo | Provenance | Air permeability |
|---|---|---|---|
| Fleece | 0.34 | Measured | very high |
| Thin knit | 0.25 | Measured | high |
| Dense wool sweater | 0.36 | Measured | moderate |
| Tightly woven shell | 0.1 | Estimated (between 0.08 and 0.13) | low |
| Membrane shell | 0.1 | Estimated (between 0.08 and 0.13) | very low |
Read the first and third rows together. A dense wool sweater carries more published insulation than a fleece and holds up better in wind, because clo is measured in still air and says nothing about whether a garment resists moving air.
The limit of this data
Stated here rather than in a footnote, because a clo table read without it looks like a ranking of warmth and is not one.
- Measured in still air. The standards measure garments on a heated manikin in still air and correct separately for air movement. Two garments with the same clo stop being comparable once there is wind on them.
- Whole-body, not local. Insulation sums across an ensemble, so a single leg garment moves whole-body comfort by about a degree. What a person actually feels is set by the coldest patch of skin, which is why bare legs in wind feel far worse than the arithmetic suggests.
- Garments vary. A tabulated value describes a representative garment, not the one in your wardrobe. Fabric weight, fit and construction all move it.
- Estimates are labelled. Where a garment is not tabulated under its own name, the value is marked estimated and the two published neighbours it sits between are shown, so the estimate can be judged rather than taken on trust.
Sources
- ANSI/ASHRAE Standard 55 — Thermal Environmental Conditions for Human Occupancy, Table 5.2.2.2, garment insulation.
- ISO 9920 — Estimation of thermal insulation and water vapour resistance of a clothing ensemble, Annex A.
Where the two differ, the ASHRAE value is used, and any garment absent from both is marked as an estimate rather than assigned a number.
Using and citing this page
The tables may be quoted with attribution to WhetherWear and a link to this page. The underlying clo values belong to the standards above and should be attributed to them; what is original here is the comparison, the bracketing of untabulated garments, and the conversion to a comfort range.
Corrections are welcome and are handled the way every other claim on the site is — see the editorial standards.
Related questions
What is a clo?
A unit of clothing insulation. One clo is roughly what a person needs to sit comfortably indoors at about 21°C, and garment values sum to give an ensemble total.
How much warmth do tights actually add?
Sheer tights add about 0.02 clo, which is roughly a fifth of an opaque tight and close to nothing in whole-body terms. Opaque tights sit near 0.1 clo and fleece-lined near 0.2, comparable to a thin trouser.
Is a fleece warmer than a wool sweater?
By published insulation a dense wool sweater is slightly higher, at about 0.36 clo against 0.34. Outdoors the gap widens, because clo is measured in still air and wool resists moving air where a raised fleece pile does not.
Can I reuse these tables?
Yes, with attribution to WhetherWear and a link to this page. The clo values themselves come from ASHRAE 55 and ISO 9920 and should be attributed to those standards.