Strawbales uniquely combine very high insulation values with very light weight, low cost, environmental footprint to produce and transport (if locally sourced), structural stability and durability, resilience and fireworthiness. Efficient use of resources (economically and environmentally) requires building materials to serve several functions at once, and strawbale construction shows excellent multi-functional qualities in this way. Conductivity values (a measure of how much heat escapes every second) are typically 0.05 W/m.K, while common insulation materials like polyurethane foam or glass wool are around 0.03 or 0.04. Brick or cement is 20 times worse, at around 1.00 W/m.K. A strawbale wall with lime or clay plaster would typically cost 1/5 of a masonry wall with foam insulation (as typically built today), and pass about half the amount of heat energy.