Mon, 25 May 2026 13:07:30 +0100 https://www.greenbuildingforum.co.uk/newforum/ Lussumo Vanilla 1.0.3 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=1668&Focus=19836#Comment_19836 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=1668&Focus=19836#Comment_19836 Fri, 02 May 2008 12:51:00 +0100 greenland https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=1668&Focus=19840#Comment_19840 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=1668&Focus=19840#Comment_19840 Fri, 02 May 2008 13:08:28 +0100 Paul in Montreal Posted By: greenlandI can't work out if it's breathable

Oh gosh, we really need to put to rest the misconception that breathable has anything to do with air movement. A GoreTex jacket is breathable, but it is wind proof. In the context of walls, breathable means vapour permeable and has nothing to do with air tightness. It's possible to have an airtight wall that is breathable - indeed, that is exactly what products like Tyvek and Typar provide - an air tightness membrane that is vapour permeable but also waterproof. Since polystyrene beads are made of expanded polystyrene, there's a good change your wall is breathable. Expanded polystyrene sheets are not considered to be a vapour barrier, but extruded ones thicker than 50mm are.

Paul in Montreal.]]>