{"id":4522,"date":"2026-04-27T14:55:51","date_gmt":"2026-04-27T14:55:51","guid":{"rendered":"https:\/\/sleepy-hofstadter.94-76-228-222.plesk.page\/nota_tecnica\/the-thermal-conductivity\/"},"modified":"2026-09-01T14:35:22","modified_gmt":"2026-09-01T14:35:22","slug":"the-thermal-conductivity","status":"publish","type":"nota_tecnica","link":"https:\/\/ediltec.com\/en\/technical-notes\/the-thermal-conductivity\/","title":{"rendered":"THE THERMAL CONDUCTIVITY"},"content":{"rendered":"
\n
\n

“`
\n
\n Thermal performance and standards
\n<\/span><\/p>\n

\n Thermal conductivity and thermal resistance of insulation materials
\n<\/h2>\n

\n The European reference standards for thermal insulation products are
\n EN 13164<\/strong> for extruded polystyrene foam (XPS) and
\n EN 13165<\/strong> for rigid polyurethane foam products.\n<\/p>\n

\n These standards define mandatory and optional tests, specimen dimensions,
\n testing frequency and the criteria used to classify the performance
\n declared by the manufacturer.\n<\/p>\n

“`<\/p><\/div>\n

\n

“`<\/p>\n

\n Each manufacturer is required to provide a
\n Declaration of Performance<\/strong>, or DoP, which specifies
\n the essential characteristics of the product, including its declared
\n thermal conductivity value.\n<\/p>\n

“`<\/p><\/div>\n

\n

“`<\/p>\n

\n How the thermal conductivity value is determined
\n<\/h3>\n

\n To determine thermal conductivity, the manufacturer collects and analyses
\n the results obtained through factory production control. The data are
\n statistically processed to determine the value to be declared in the
\n product’s technical documentation.\n<\/p>\n

\n The declared value must provide a conservative representation of the
\n insulation performance over time and not only the performance measured
\n immediately after production.\n<\/p>\n

“`<\/p><\/div>\n

\n

“`<\/p>\n

\n


\n \u03bb
\n <\/span><\/p>\n

\n Thermal conductivity
\n <\/h3>\n

\n Thermal conductivity measures a material’s ability to conduct heat
\n and is expressed in W\/mK<\/strong>.\n <\/p>\n

\n The lower the \u03bbD<\/strong> value, the greater the insulating
\n effectiveness of the material.\n <\/p>\n<\/article>\n

\n


\n DoP
\n <\/span><\/p>\n

\n Declared value
\n <\/h3>\n

\n The value stated in the Declaration of Performance is derived from
\n product testing and the statistical processing of the results.\n <\/p>\n

\n The declaration provides designers with technical data that can be
\n verified and compared.\n <\/p>\n<\/article>\n

\n


\n R
\n <\/span><\/p>\n

\n Thermal resistance
\n <\/h3>\n

\n Thermal resistance indicates the ability of a layer of material
\n to resist the flow of heat.\n <\/p>\n

\n The higher the R<\/strong> value, the greater the insulating
\n performance of the layer being considered.\n <\/p>\n<\/article>\n

“`<\/p><\/div>\n

\n

“`<\/p>\n

\n Initial thermal conductivity and stabilised value
\n<\/h3>\n

\n For some insulation materials, the thermal conductivity measured
\n immediately after production may differ from the value measured after
\n a certain period of time. Over time, the value tends to stabilise until
\n it reaches the performance level used for declaration purposes.\n<\/p>\n

\n For this reason, product standards establish specific procedures for
\n assessing declared thermal conductivity and taking into account changes
\n in performance over time.\n<\/p>\n

\n
\n
\n PIR polyurethane
\n <\/span><\/p>\n

\n The declared value is determined according to the ageing and
\n control procedures specified by
\n EN 13165<\/strong>.\n <\/p>\n<\/p><\/div>\n

\n
\n XPS extruded polystyrene
\n <\/span><\/p>\n

\n The declared value is assessed according to the procedures and
\n timeframes defined by
\n EN 13164<\/strong>, also depending on thickness.\n <\/p>\n<\/p><\/div>\n<\/div>\n

“`<\/p><\/div>\n

\n

“`<\/p>\n

\n Verification and updating of declared values
\n<\/h3>\n

\n To determine declared thermal conductivity, the manufacturer must have
\n an adequate number of results obtained through internal measurements
\n or tests carried out by external laboratories.\n<\/p>\n

\n The results are periodically reviewed to ensure that the value stated
\n in the technical documentation continues to accurately represent
\n production performance.\n<\/p>\n

\n The statistical thermal conductivity value is declared using conservative
\n criteria and is normally stated in increments of
\n 0.001 W\/mK<\/strong>.\n<\/p>\n

“`<\/p><\/div>\n

\n

“`
\n
\n Rounding example
\n<\/span><\/p>\n

\n If the result of the statistical analysis is
\n 0.033645 W\/mK<\/strong>, the declared value will be
\n 0.034 W\/mK<\/strong>.\n<\/p>\n

“`<\/p><\/div>\n

\n

“`<\/p>\n

\n How thermal resistance is calculated
\n<\/h3>\n

\n The thermal resistance of an insulation layer is calculated by dividing
\n the thickness of the material, expressed in metres, by its thermal
\n conductivity value.\n<\/p>\n

\n


\n Formula
\n <\/span><\/p>\n

\n R = d \/ \u03bb\n <\/div>\n

\n R expressed in m2<\/sup>K\/W \u00b7 d expressed in metres \u00b7 \u03bb expressed in W\/mK\n <\/p>\n<\/div>\n

“`<\/p><\/div>\n

\n

“`<\/p>\n

\n Calculation example
\n<\/h3>\n

\n Considering an insulation material with a thickness of 80 mm<\/strong>
\n and a declared thermal conductivity of 0.036 W\/mK<\/strong>:\n<\/p>\n

\n
\n
\n Calculation
\n <\/span>
\n
\n 0.080 \/ 0.036 = 2.22 m2<\/sup>K\/W
\n <\/strong>\n <\/div>\n
\n
\n Declared value
\n <\/span>
\n
\n RD<\/sub> = 2.20 m2<\/sup>K\/W
\n <\/strong>\n <\/div>\n<\/div>\n

“`<\/p><\/div>\n

\n

“`<\/p>\n

\n Declared values for thickness groups
\n<\/h3>\n

\n In some cases, a single thermal conductivity value is declared for
\n a group of thicknesses. This value represents a conservative performance
\n level applicable to all products included within the group.\n<\/p>\n

\n A specific thickness may therefore have an actual thermal conductivity
\n that is better than the general value declared for the group. The thermal
\n resistance value stated for each thickness must nevertheless be determined
\n on the basis of the performance applicable to that product.\n<\/p>\n

“`<\/p><\/div>\n

\n

“`<\/p>\n

\n Independent quality controls
\n<\/h3>\n

\n In addition to the controls required by the production system, Ediltec
\n periodically submits its products to assessments carried out by qualified
\n external laboratories and organisations.\n<\/p>\n

\n For the X-FOAM\u00ae<\/strong> range, representative production samples
\n are tested by the German institute
\n FIW M\u00fcnchen<\/strong>, a leading European organisation in the field
\n of thermal insulation materials.\n<\/p>\n

“`<\/p><\/div>\n

\n

“`
\n
\n Indicative comparison
\n<\/span><\/p>\n

\n Thermal conductivity values of selected insulation materials
\n<\/h3>\n
\n\n\n\n\n\n\n\n\n\n\n
\n Insulation material\n <\/th>\n\n Indicative thermal conductivity W\/mK\n <\/th>\n<\/tr>\n<\/thead>\n
\n POLIISO\u00ae with impermeable facings<\/strong>\n <\/td>\n\n 0.022\u20130.023\n <\/td>\n<\/tr>\n
\n POLIISO\u00ae with permeable facings<\/strong>\n <\/td>\n\n 0.025\u20130.028\n <\/td>\n<\/tr>\n
\n X-FOAM\u00ae XPS<\/strong>\n <\/td>\n\n 0.029\u20130.038\n <\/td>\n<\/tr>\n
\n Fibrous insulation products\n <\/td>\n\n 0.035\u20130.044\n <\/td>\n<\/tr>\n
\n Wood fibre\n <\/td>\n\n 0.038\u20130.050\n <\/td>\n<\/tr>\n
\n Blonde cork\n <\/td>\n\n 0.037\u20130.054\n <\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<\/div>\n

\n The values shown are indicative and may vary depending on product type,
\n thickness, facing and the relevant Declaration of Performance.\n<\/p>\n

“`<\/p><\/div>\n<\/section>\n","protected":false},"author":1,"featured_media":0,"template":"","meta":{"_yoast_wpseo_focuskw":"the thermal conductivity","_yoast_wpseo_title":"THE THERMAL CONDUCTIVITY","_yoast_wpseo_metadesc":"The European norm of reference of the product \"Extruded Polystyrene - XPS\" is EN 13164 and the European norm of reference of the \"Polyu","id_tipo":"","id_traduzione":"","titolo":"","testo":"","ordine":"2","visibile":"1","immagine":"","prodotti_consigliati":"","seo_link":"the-thermal-conductivity","seo_title":"","seo_keywords":"","seo_description":"","_bridge_tax_data":"[]","_bridge_imported":"1","_bridge_source":"laravel_bridge","meta_vantaggi":"","meta_posa_opera":"","meta_avvertenze":"","tipo":"","_bridge_import_key":"3_nota_tecnica_EN","id_nota_tecnica":"3","id_download":"","file_pdf":0,"id_comunicazione":"","data":"","anno":"","prefisso":"","img":"","id_news":"","alt_text":"","top":"","link":"","link_click":"","galleriaMedia_news":"","id_prodotto":"","_sku":"","nuovo":"","brochure_pdf":0,"certificazione_pdf":0,"proprieta":"","titolo_applicazione_parent":"","brochure":"","titolo_en":"","click":"","seo_link_salva":"","alt_text_salva":"","galleria_media":"","_product_image_gallery":"","certificazioni_pdf":0,"lingua":"","Matchi_en":"","brochure_link":"","certificazione_link":"","_regular_price":"","_sale_price":"","_price":"","_stock":"","_stock_status":"","_sale_price_dates_from":"","_sale_price_dates_to":"","galleria_captions":"","immagine_didascalia":"","_bridge_translation_key":""},"tags":[1944,1945],"class_list":["post-4522","nota_tecnica","type-nota_tecnica","status-publish","hentry","tag-thermal-conductivity","tag-thermal-insualtion"],"yoast_head":"\nTHE THERMAL CONDUCTIVITY<\/title>\n<meta name=\"description\" content=\"The European norm of reference of the product "Extruded Polystyrene - 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