There is an increasing interest in giving added value to forestry by-products. Forest biomass residues can be a rich source of useful raw materials. The usage of Eucalyptus species in forestry has increased markedly over the last decades and these plantations currently cover approximately 20 million hectares worldwide. The industrial transformation of both Eucalyptus sp. Pulp and solid wood, generates high volumes of bark as a by-product, which is mainly used as fuel or taken to landfill. Particularly, Eucalyptus globulus bark has a fibrous morphology that can be used to manufacture novel bio-based products. In this work, we developed a rigid thermal insulation panel for construction applications. It is primarily based on Eucalyptus bark fibers (90% w/w), as well as synthetic fibers (10% w/w). The raw material was supplied by a Chilean sawmill. After debarking, the bark was mechanically treated in a hammer mill. Then, the fibers were introduced to a variable-speed fiber opening machine to evaluate the process. The mixed fibers were transported to an airlay system fixing the objective density. The Eucalyptus bark fibers were characterized morphologically and mechanically. Thermal conductivity and mold resistance of the panels were tested. The samples exhibited thermal insulation properties, with thermal conductivity values ranging between 0.038–0.04 W/m K. However, the panels displayed low mold resistance, due to the chemical composition of Eucalyptus bark. Valuable knowledge in Eucalyptus Globulus bark processing was obtained, which may contribute to the increase of new fiber sources and their applications.