Retention is a papermaking term describing the ability to separate fibres from water to form a paper sheet.  Good retention is essential for economical and fast paper production.

One of the most controlled parameters in the papermaking process is retention.  Increased retention reduces the amount of papermaking compounds, fibres and fillers in the waste water and improves profitability. 

To increase the fibre and filler retention in the  papermaking process, aluminium salts, sodium aluminate (SAL) and poly aluminium chloride (PAC) are used.  Aluminium salts enhance the effect of other process chemicals such as polyelectrolytes and removes unwanted, so called, anionic trash.