Calculating Clothing Insulation

Introduction

Clothes should provide the correct amount of insulation 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

Bra	0.01
Panties	0.03
Briefs	0.04
Boxer Briefs	0.10
Long Johns	0.15
Singlet	0.04
Undershirt	0.09
Undershirt with long sleeves	0.12

Shirts/Blouses

Short sleeves	0.15
Light-weight, long sleeves	0.20
Normal, long sleeves	0.25
Flannel shirt, long sleeves	0.30
Light-weight blouse, long sleeves	0.15

Trousers

Shorts	0.06
Light-weight	0.20
Normal	0.25
Flannel	0.28

Dresses/Skirts

Light skirts (summer)	0.15
Heavy skirt (winter)	0.25
Light dress, short sleeves	0.20
Winter dress, long sleeves	0.40
Boiler suit	0.55

Sweaters

Sleeveless vest	0.12
Thin sweater	0.20
Sweater	0.28
Thick sweater	0.35

Jackets

Light, summer jacket	0.25
Jacket	0.35
Smock	0.30

High-insulative, fibre-pelt

Boiler suit	0.90
Trousers	0.35
Jacket	0.40
Vest	0.20

Outdoor clothing

Coat	0.60
Down jacket	0.55
Parka	0.70
Fibre-pelt overalls	0.55

Sundries

Socks	0.02
Thick, ankle socks	0.05
Thick, long socks	0.10
Nylon stockings	0.03
Shoes (thin soled)	0.02
Shoes (thick soled)	0.04
Boots	0.10
Gloves	0.05

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:

I_a = 1 / (0.61 + 1.9 × √w)

where:

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

Insulation of boundary air layer, I_a, for different wind speeds

Wind	mph	km/h	m/s	`I_a` (clo)
Calm	< 1	< 2	< 0.5	> 0.5
Light air	1–3	2–5	0.5–1.5	0.4
Light breeze	4–7	6–11	1.6–3.3	0.3
Gentle breeze	8–12	12–19	3.4–5.5	0.2
Moderate breeze	13–18	20–28	5.6–7.9	0.2
Fresh breeze	19–24	29–38	8–10.7	0.2
Strong breeze	25–31	39–49	10.8–13.8	0.1
High wind	32–38	50–61	13.9–17.1	0.1
Gale	39–46	62–74	17.2–20.7	0.1
Violent	> 47	> 75	> 20.8	< 0.1