Shredded mattress waste was valorised into an insulation material via the addition of a cellulose/urea gel. The addition of the cellulose-based gel was found to successfully bond the miscellaneous shred, creating a composite with a unique pore structure. The composites were tested for their thermal conductivity to explore their use as insulation materials in construction applications. From the testing, the thermal conductivity was found to range between 49 and 60 mW/mK depending on the composition and processing steps. While some of the produced composites showed poor thermal resistance not suitable for an insulation product, we report that additional processing resulted in thermal conductivities that were lower than the existing commercial insulation product (45 mW/mK). Numerical simulations revealed that it is possible to further reduce the thermal conductivity of the samples by optimising the porosity and pore sizes. Hence, there is a strong promise of recycling a common waste product into sustainable building insulation products with further optimisations.