Nano-structured silica with an open network structure has been produced by controlled precipitation from geothermal water. The material has a pore volume, as measured by the oil absorption capacity of about 200-250 g oil. 100 g(-1) silica, and the surface area is about 50-60 m(2) g(-1). It has been used as a filler in newsprint and the technology has been developed on a laboratory scale and progressed to pilot plant production with full scale paper mill manufacturing and commercial printing trials. Print through reductions of 30% for newsprint and 40% for yellow directory grade paper were achieved. Nano-structured calcium silicate with an open framework structure has been formed from sodium silicate solution. This product has a very large pore volume of about 300-550 g oil. 100 g(-1) silicate and a large surface area of about 350-600 m(2) g(-1) depending upon the synthesis method. It has been tested as a filler in newsprint on a laboratory scale and reduced print through by about 40% for 55 gsm newsprint and by about 53% for 45 gsm newsprint. The material is better than nano-structured silica for this application and it substantially outperforms calcined clay. (C) 2003 Elsevier B.V. All rights reserved.