Calculating Clothing Insulation

Introduction

Clothes should provide to maintain a stable body temperature and achieve thermal comfort.

In addition to the clothing insulation, some additional insulation is gained from the air just outside the outermost garment – the boundary air layer – which contributes to the total insulation.

The precise measurement of garment insulation is done on a thermal mannikin in a lab. Lacking this equipment, we can estimate the insulation from either: calculating the insulation based on the type and density of insulation materials used to make the garment; or for common types of everyday clothes, we can look up values that are published by standards bodies.

Calculation for Outdoor Clothes

Richard Nisley has been kind enough to measure and publish the insulation of various fabrics and materials used in cold-weather clothing. Using Mr. Nisley’s figures, we can estimate the intrinsic insulation of any garment made with similar materials.

Values for Common Garments

Underwear

Bra0.01
Panties0.03
Briefs0.04
Boxer Briefs0.10
Long Johns0.15
Singlet0.04
Undershirt0.09
Undershirt with long sleeves0.12

Shirts/Blouses

Short sleeves0.15
Light-weight, long sleeves0.20
Normal, long sleeves0.25
Flannel shirt, long sleeves0.30
Light-weight blouse, long sleeves0.15

Trousers

Shorts0.06
Light-weight0.20
Normal0.25
Flannel0.28

Dresses/Skirts

Light skirts (summer)0.15
Heavy skirt (winter)0.25
Light dress, short sleeves0.20
Winter dress, long sleeves0.40
Boiler suit0.55

Sweaters

Sleeveless vest0.12
Thin sweater0.20
Sweater0.28
Thick sweater0.35

Jackets

Light, summer jacket0.25
Jacket0.35
Smock0.30

High-insulative, fibre-pelt

Boiler suit0.90
Trousers0.35
Jacket0.40
Vest0.20

Outdoor clothing

Coat0.60
Down jacket0.55
Parka0.70
Fibre-pelt overalls0.55

Sundries

Socks0.02
Thick, ankle socks0.05
Thick, long socks0.10
Nylon stockings0.03
Shoes (thin soled)0.02
Shoes (thick soled)0.04
Boots0.10
Gloves0.05

Boundary Air Insulation

The thin layer of air held on the outside of the clothes by frictional drag adds some insulation. Indoors, with slight air movement of around 0.1 m/s, this is fairly significant; outdoors, with increasing air movement due to wind, this effect is much less pronounced.

The wind-adjusted boundary air insulation formula from Fourt and Hollies Clothing: Comfort and Function (1970) is:

Ia = 1 / (0.61 + 1.9 × √w)
where:

Ia = insulation of boundary air layer (clo)
w = wind speed (m/s)

Insulation of boundary air layer, Ia, for different wind speeds
Windmphkm/hm/sIa (clo)
Calm< 1< 2< 0.5> 0.5
Light air1–32–50.5–1.50.4
Light breeze4–76–111.6–3.30.3
Gentle breeze8–1212–193.4–5.50.2
Moderate breeze13–1820–285.6–7.90.2
Fresh breeze19–2429–388–10.70.2
Strong breeze25–3139–4910.8–13.80.1
High wind32–3850–6113.9–17.10.1
Gale39–4662–7417.2–20.70.1
Violent> 47> 75> 20.8< 0.1

Further Reading

Check that the insulation of your clothes matches .

A practical system of units for the description of the heat exchange of man with his environment, Gagge, Burton & Bazzett (1941)
Defines the clo unit for thermal insulation. A short (two page) and accessible paper.
ANSI/ASHRAE Standard 55: Thermal Environmental Conditions for Human Occupancy
ISO 9920, Ergonomics of the thermal environment—Estimation of the thermal insulation and evaporative resistance of a clothing ensemble (2003)
Contain tables of metabolic rates for different activities and lists of insulation values for various garments.