What is carpet tog?
A 'tog' is the unit of measurement we use to show a material's - or carpet's - thermal insulating property. In short form, the higher tog value a material or carpet has, the more it will retain heat and the better it will be at insulating. Tog is very important in the flooring world depending on your needs - higher tog will help insulate a home better, but lower tog will work better with underfloor heating. The overall tog value of a chosen flooring option will also include the underlay - so choices will often be influenced by budget and (as mentioned) underfloor heating presence.
In general, the type of flooring influences tog thus; the denser the pile construction of the carpet, and the heavier the pile weight, the greater the tog value. Tog tends to range between 0.70 to over 3.00.
Which value is best for me?
The best rule of thumb is: lower tog is good if underfloor heating is presence, but higher tog otherwise will help insulate a home and keep it warm. Higher tog carpet combined with underfloor heating is no disaster - it will simply slow the heat transfer from the heating system to the room above.
Wool carpets have a higher tog rating naturally than other fibres, as do foam underlays over felts.
Other considerations, such as to the weight of the carpet, should also be considered when buying flooring.