New insulation fiberboards from sunflower cake with improved thermal and mechanical properties were produced by pressing at ambient temperature. Best compromise between mechanical and heat insulation properties (λ = 77.6 mW/m K at 25°C) was a starch-based board with 20% binder content. Because of its promising heat insulation properties, this new fiberboard could be positioned on walls and ceilings for thermal insulation of buildings. The bulk cake was an even better insulation material (only 62.0 mW/m K for thermal conductivity at 25°C): usable as loose fill in the attics of houses.