For instance, a water molecule may be small enough to pass through the pores while larger molecules are not, so water is forced into the pores which act as a trap for the penetrating water molecules which are retained within the pores.
A water molecule may be small enough to pass through the pores. This is for instance. Water is forced into the pores. This was for instance. This pores act as a trap for the penetrating water molecules. These penetrating water molecules are retained within the pores. Larger molecules are not.