Silica-based sols

2222The invention relates to an aqueous sol containing silica-based particles which sol has a specific surface area of at least 115 m/g aqueous sol and an S-value within the range of from 10 to 45% or contains silica-based particles having a specific surface area of at least 550 m/g and less than 1000 m/g SiO. The invention further relates to processes for the production of said aqueous sol and the use of the aqueous sol containing silica-based particles as a drainage and retention aid in the production of paper as well as a process for the production of paper from an aqueous suspension containing cellulosic fibres, and optional filler, in which silica-based particles and at least one charged organic polymer are added to the cellulosic suspension.