Perma-Seal log air and wind barrier was developed here in Ireland and is used between each layer of log on all residential and large 70mm log cabins. Perma-Seal is unique to our cabins and works in the following way. Logs swell in winter and shrink in summer this is natural for all wood. The Perma-Seal system was designed with this in mind and pushes itself down tight between the logs in winter keeping them sealed tight from the elements. In summer when the logs shrink it expands and again seals the gaps between the logs. It is made up of a foam substance that works and has been used all over America and Canada on cabin structures for years.