<p>The invention provides a concrete or cementicious product having one or more forms of carbon dispersed therethrough so as to reduce thermal conductance across the product. The one or more forms of carbon are preferably dispersed therethrough in small clusters and/or agglomerates that are wholly or substantially isolated from each other. The carbon(s) have a BET surface area of less than 550 m<2>/g and include(s) carbon black. The invention also provides a method of forming such a concrete or cementicious product.</p>