An article includes walls defining an insulating space therebetween and a vent forming an exit for gas molecules during evacuation of the space. A distance separating the walls is variable in a portion adjacent the vent such that gas molecules are directed towards the vent imparting a greater probability of molecule egress than ingress such that deeper vacuum is developed without requiring getter material. The variable-distance portion may be formed by converging walls. Alternatively, a portion of one of the walls may be formed such that a normal line at any location within that portion is directed substantially towards a vent opening in the other wall.