ABSTRACT: New lightweight granular materials, called '3I' loose-fill materials (Inorganic, Insulating and Incombustible), were developed in the LEEMA-EU project. They are based on inorganic polymers derived from mineral tailings, recycled glass and industrial by-products and are produced as lightweight hollow aggregates. They have superior thermal conductivity, reduced embodied energy and lower cost compared to currently applied bulk insulation products. They can be used for the insulation of cavity walls or between rafters to meet energy regulations. They are also used as lightweight aggregates in boards or blocks and filling of masonry block perforations. In this paper the focus is on their application as grains in cavity walls using a blowing machine. Two types of walls were studied: existing double-leaf masonry walls and new lightweight timber-frame walls. The thickness of the air space and the size of the holes for blowing the grains differ considerably for both applications. The aim of the test program was to study the feasibility of using existing blowing machines.