Nano titanium dioxide (TiO2) with excellent capabilities of refraction and absorption has been acknowledged as an efficient enhancer of radiative thermal insulation performance of fibrous materials. Based on the layer-by-layer (LBL) assembling technique, nano TiO2 was successfully assembled on the fibre surface of fibrous insulations to form nano TiO2 assembled fibrous insulations. To obtain quantitative predictions of radiative thermal insulation enhancement of nano TiO2 on fibrous insulations, numerical methods of radiative thermal properties were presented by combining the Rosseland equation, precise Mie theory and subtractive Kramers-Kronig relation. For validation purposes, we fabricated samples with different loading levels of nano TiO2 and observed good agreement of radiative thermal conductivity between the measurements and our predictions. The fundamental parameters of the numerical method, including fibre diameter, loading level of nano TiO2 and infrared transmittances, were experimentally measured through scanning electron microscopy (SEM), thermogravimetric (TG) analysis and Fourier transform infrared (FTIR) spectroscopy, respectively. The influence of loading nano TiO2 was analysed, which presented an almost 43% reduction of the radiative thermal conductivity when the loading level of nano TiO2 was 5.7 wt.%. The effect of fibre diameter on radiative thermal properties was also investigated to minimize the radiative thermal conductivity. A further 6% reduction of radiative thermal conductivity was predicted by optimizing the fibre diameter. The optimal fibre diameter was decreased from 1.7-2.0 mu m for pure fibrous insulations to 0.9-1.0 mu m for nano TiO2 assembled fibrous insulations, which fell within the nanometre scale and could be implemented by using electrospinning technique in experiment. The methods of loading nano TiO2 and optimizing the diameter of fibrous insulations demonstrated in this paper could serve as very useful references for enhancing radiative thermal performance and reducing heat loss in practical engineering applications. (C) 2017 Elsevier Ltd. All rights reserved.