Paper is highly porous, and for this reason it is particularly prone to absorbing odours. It is essential that papers are stored away from any contaminants, in an airtight container. Similarly, because they are prone to mildew they must be kept dry. You should give your filter paper the same attention you give to your coffee beans.
When low-quality paper gets wet, such as the sort used for newspapers, it tears easily. To avoid this occurrence, filter papers are often manufactured with the addition of wet strength agents to strengthen them. One system often used for coffee filter papers are wet strength resins. The mechanical process that creates the paper of this sort uses what are known as wet lay machines which disperse the cellulose fibres and water into a slurry that is used to form the sheets of paper.
According to the Handbook of Nonwoven Filter Media, ‘Several types of resin or chemical agents can be added to the fibre slurry or stock to enhance the strength of the web after it is dried. Most often, these are cationic agents that use ionic chemistry to be attracted to the negatively charged anionic fibres’ (Irwin M. Hutte, 2007). Hutte points out that coffee filter papers are often created with the addition of wet strength resins, though it is unclear which manufactures use this method.
Filter papers have a distinctive ruffled texture known as creping. This texture increases the available surface area of the filter and the flexibility of the paper (Irwin M. Hutte, 2007). The main purpose creping serves is to reduce muddying (the situation in which a filter is clogged by fines). A thicker, creped surface increases the number of pores at the interface between the coffee bed and the paper, which makes it less likely that all the pores will be blocked.