What JIS L 1099 Tells You About Breathability
Vapour permeability figures, why the method letter matters and how to compare styles fairly.
The number and its unit
JIS L 1099 measures moisture vapour transmission rate, reported in grams per square metre per 24 hours. A style quoted at 16,000 g/m2/24h passed that much water vapour through a square metre of fabric in a day under the test conditions.
Method B-1 and why it is quoted
The standard contains several methods and they do not produce the same numbers. B-1 is the method quoted across our range. When you compare two suppliers, check that the method letter matches before you compare the figures, otherwise you are comparing two different tests.
Reading it with the water column
Water resistance and vapour permeability pull against each other in fabric construction. A specification that quotes a very high water column and a low vapour figure describes a garment that will feel clammy in activity. Styles in our range pair figures such as 15,000mm with 3,000 g/m2/24h at one end and 10,000mm with 16,000 g/m2/24h at the other, which are two genuinely different garments.
Where the figure stops helping
Laboratory vapour transmission does not capture ventilation design. Pit zips, mesh linings and two-way front zips move more air than a small difference in the tested figure will.
More Guides
How to Read a JIS L 1092 Water Resistance Figure
What the water column number on an outerwear specification means, and what it does not tell you.
Read the guide →What an OCS Scope Certificate Covers
The difference between a scope certificate and a transaction certificate, and what a buyer should collect.
Read the guide →PFC Free Water Repellent Finishes and What Changes
Why buyers are moving away from fluorinated repellents and what to expect in wear and care.
Read the guide →Down and Synthetic Insulation Compared for Buyers
Warmth for weight, loft recovery, price and packing, and where blended fills sit between the two.
Read the guide →Two Layer and Three Layer Laminates in Outerwear
How the layer count changes weight, hand feel, durability and what the garment costs to make.
Read the guide →Frequently Asked Questions
Can I compare a JIS figure with a RET figure?
Not directly. They are different test principles and a conversion is an approximation at best.
Which figure should I specify?
Set it against end use and ask the supplier to quote the method letter alongside the number.
Have a Question This Guide Did Not Answer?
Email the question with the style number or specification you are working on and we will answer it directly.