A tog (thermal overall grade) is a unit of measurement for the thermal resistance of a material, originally developed by the Shirley Institute. Put simply, the higher a material’s tog rating, the more heat that it will retain, and the better it will be as an insulating material. A material with a high tog value would make an excellent winter coat, as it would retain a large proportion of your body’s heat while wearing it, while a coat manufactured from a low tog rated material would be better suited for use in warmer seasons, as it would allow a far greater amount of your body’s heat to radiate away while being worn.
In more technical terms, a tog equates to ten times the temperature difference, measured in °C, between two surfaces of a given material, when the flow of heat is equal to one watt per square meter. Therefore, in the case of a flooring underlay, the tog rating refers to the difference in temperature between the top and bottom layers.
Being mindful of the tog rating during the selection process will ensure you choose the right product that gives best possible opportunity to either retain as much heat as possible within the room, or to allow easy transfer of heat through the floor and into the room, for installations with underfloor heating.
For installations without underfloor heating, if you are aware the area in the home your new floor is to be installed in is perhaps quite cold in winter months, looking for products that have a high tog value will give you best opportunity to retain as much heat within the room as possible during these months. Thick carpet with a dense underlay would be our best recommendation here.
The opposite is true with those using underfloor heating. In these instances it is best that you look out for products that have low tog ratings to ensure as much heat transfer through the floor from the underfloor heating as possible. We would recommend a hard floor installation, preferably one that can be glued straight down to the subfloor as these floors and install types are best for optimum heat transfer. Carpet installations are still OK, though it's worth reading the user guide of your underfloor heating system to find out what their max tog rating is. Typically it'll be no more than 2.50. If you are opting for a carpet installation with underfloor heating, we'd recommend Duralay King underlay as the Tog rating is very low at 0.80, leaving plenty of room for selecting your carpet.