Tog and Clo ratings, the standard systems used to measure a materials insulation capability, in particular that of duvets, have long confused shoppers. These measurements are rarely used outside of a select few industries, and as such our familiarity with them is minimal. So, what do all the various numbers mean?
The tog rating system is the standard insulation measurement used in the UK and Europe, and is found by placing the duvet on a metal plate at room temperature in controlled conditions. By measuring the heat lost through the duvet, a rating can be assigned to the material.
Duvets are available anywhere from 1 tog to 18, although generally the lowest you will see is 1.5 and the highest 15. Which to go for will depend on a few variables, such as how cold you tend to feel and the time of year you are buying for. For summer, a rating of 1.5 – 4.5 is recommended. In autumn aim for roughly 9, while a 12 – 13.5 will be ideal for winter.
These figures aren’t set in stone, and the best rating for you will depend on, well, you. Many people, instead of changing their duvet multiple times a year, will either stick with a middle ground of around 9 all year, or buy a set of various differently rated duvets that can be attached together using buttons or Velcro. This turns a single duvet into an adaptable option to keep you suitably warm all year.
The Clo rating system, although essentially just measuring the same thing for customers in the US, works a little differently and is most simply explained in terms of clothing. One tog is defined as the amount of clothing needed to maintain a person’s comfort in a room at 21°C, with humidity below 50% and a wind velocity of 250cm/s.
Clo ratings range from 0-4. One clo is equivalent in value to 1.55 tog, a rating of 0 applies to a completely naked person and a high of 4 would relate to thick fur clothing like the traditional image of the Eskimo.
To put that into more useful terms, the recommended rating for summer clothing is around 0.6, while a clo rating of 1 is best for your standard winter clothing. For ski trips, mountaineering, expeditions and the like, you’ll need something a bit warmer.
Armed with this knowledge, your next duvet purchase should be a little more straightforward, so no more Rhod Gilbert-esque breakdowns in the middle of Dunelm.
Sam is an aspiring novelist with a passion for fantasy and crime thrillers. He is currently working as a content writer, journalist & editor in an attempt to expand his horizons.