We have fabricated amorphous polymer composites with ultralow silica contents (e.g., 0.1 wt %), without nano- or microclusters but with silica units distributed quasi-regularly within the polymer network matrix. This fact and other data obtained imply the existence of subnanometer-sized silica nodes (SNSSN) only in this case which are connected covalently with the matrix, i.e., the formation of the hybrid sub-nanocomposites. In this work, the densely cross-linked Cyanate Ester Resins (CER)-based composites with 0.1-10 wt % silica, introduced by a sol-gel method, were synthesized and investigated by HAADF STEM, EDXS, far-IR spectroscopy, DMA and DSC. The obtained subnanocomposites manifest an extremely high "constrained dynamics" effect and superiority in thermal and mechanical properties compared to those of the nanocomposites with higher silica contents. (C) 2016 Elsevier Ltd. All rights reserved.