internal temperature of the board should be brought to at least 400 u00b0 f for at least 10 sec again the nature of the heat source is not important following the heat treating step and while the paper is still hot water is applied to it preferably by spraying even though one effect of the water application is to cool the paper it is important that the paper not be allowed to cool substantially before the water application paper temperature must remain above 100 u00b0 c until water is applied thereafter the heat treated and rewetted paper is then cooled conditioned and calendered according to conventional procedure the invention has been practiced as described in the following examples the improvement in board quality will be apparent from an examination of the test results listed in the tables below a bleached kraft board with ambient moisture content of 5 0 no ht was tested for various properties of interest in both the machine direction 34 md 34 in the table and the cross machine direction 34 cd 34 a portion of the board was then heat treated at 410 u00b0 f 210 u00b0 c for 15 seconds 34 ht 34 a portion of the heat treated board was immediately rewetted to 10 6 moisture content and then dried conventionally ht and rw both samples were conditioned for 48 hours at 70 u00b0 f 21 u00b0 c 65 relative humidity and were then tested properties of these samples are given in table i.