the process of the invention comprises increasing the moisture content of a cellulosic fiber - containing fabric to above 20 % by weight so that the fibers are substantially completely swollen in the presence of a catalyst and then introducing the fabric into formaldehyde vapors in a treating chamber and curing to improve the wrinkle resistance of the fabric . the fabric may be impregnated with an aqueous solution of the catalyst and then treated with formaldehyde vapors . the invention does not use limited amounts of moisture to control the most efficient in the most highly swollen state of the cellulose fiber . the relatively high amount of water present allows more efficient conversion of formaldehyde to the hydrate which is the cross - linker . thus , optimum results can be obtained with much less formaldehyde . during the crosslinking reaction at the curing stage , moisture is given up from the fabric as the cross - linking occurs , resulting in a decrease in the moisture content of the fabric . in fabrics having a moisture content of 20 % or less , this tends to lower the effectiveness of the cross - linking reaction requiring higher concentrations of formaldehyde . in the process of the present invention , moisture is given up from a high level , that is , greater than 20 %, preferably greater than 30 %, e . g ., from 60 - 100 % or more , and the cross - linking is optimized . moisture which is so difficult to control , is not a problem in the present invention which only requires that the moisture content be above 20 % which is simple to insure . of course , water is not allowed to be present in so much of an excess as to cause the catalyst to migrate on the fabric . the necessary moisture may be applied to the fabric by any conventional technique . it may be added separately or in the form of an aqueous solution of the selected catalyst , as by padding , fogging , spraying or the like . a fog spray will achieve high moisture content in a very short time . in addition , water spray or fog insures uniform moisturization . in the present process , the amount of catalyst used controls the cross - linking . preferably , an aqueous solution of the catalyst is padded onto the fabric so as to supply both the catalyst and the moisture in one operation . of course , a spray technique could also be used . a wide range of liquid and gaseous acid catalysts may be used in the present process since the cross - linking is optimized by the high moisture content and fully swollen condition of the fibers . such acid catalysts include hydrochloric acid , hydrobromic acid , hydroiodic acid , nitric acid , nitrous acid , hypophosphorus acid , orthophosphorus acid , pyrophosphorus acid and the like acids . sulfurous acid which contains dissolved sulfur dioxide may also be used . any gaseous catalyst which is used is first dissolved in an aqueous solution and then applied to the fabric which is then treated with formaldehyde vapor to effect cross - linking . the amount of catalyst may vary depending upon the particular type and the desired characteristic of the final fabric . however , in general the catalyst is incorporated in the fabric . however , in general the catalyst is incorporated in the fabric , on a dry weight basis , in an amount within the range of from 0 . 1 % to about 3 . 5 %, preferably about 0 . 1 - 0 . 5 %. for sulfurous acid , a range of from 1 . 5 % to 3 . 5 % is preferred . the catalyst may be applied to the fabric from an aqueous solution by conventional techniques , preferably such as padding or spraying . the ph of the aqueous solution is of course in the acid range . padding is the preferred method of application since the amount of solution applied can be carefully controlled . the fabric may be continuously precured by first applying the aqueous catalyst solution to the fabric , adding additional moisture if necessary , and then exposing the fabric to formaldehyde vapors . the concentration of the catalyst solution may be such as to supply with the catalyst that amount of water necessary to fully swell the cellulose fibers without further addition to moisture . exposure to the formaldehyde vapors in this case is usually substantially immediately after the catalyst is applied to the fabric . only two process steps are necessary , application of catalyst solution and treatment with formaldehyde vapors at the proper curing temperature . of course , the fabric may be first formed into a garment and then impregnated with an aqueous solution of the acid catalyst followed by exposure to formaldehyde vapors . again , the aqueous catalyst solution must contain sufficient water to fully swell the cellulose fibers or moisture must be added . as indicated , the high moisture content in the fabric fully swells the cellulose fibers and optimizes the cross - linking reaction thereby providing improved crease resistance . accordingly , considerably less formaldehyde is required than in the known vapor processes . this results in a direct reduction in the cost of the process . moreover , due to the lower concentration of formaldehyde required , less excess formaldehyde is found on the fabric after treatment and the extent to which washing or steam cleaning is required is minimized . the formaldehyde concentration in the treatment chamber is from about 1 . 0 % to about 6 . 5 % by volume , preferably about 1 . 0 % to 3 . 0 %. the dry add - on by reaction of the formaldehyde with the fabric at this concentration is generally less than about 0 . 5 %. at concentrations of formaldehyde below about 1 % by volume in the treatment chamber the wash appearance and crease resistance become less satisfactory than desired . at concentrations of much above about 3 % there is usually no significant increase in these properties . the utilization of small concentrations of formaldehyde in the treating chamber significantly reduces the fire hazard presented by formaldehyde since formaldehyde tends to be explosive in concentrations of 7 % by volume or above when mixed with air . the curing temperature at which the final cross - linking takes place is in the range of from about 200 ° f . to about 250 ° f ., preferably about 212 ° f . to 245 ° f . advantageously , it should be at least about 230 ° f . for the sulfurous acid system to insure that there is sufficient cross - linking to provide the necessary wrinkle resistance in the fabric . temperatures above 325 ° f ., as conventionally employed in resin curing , do not improve the present process and may serve to degrade the fabric by the action of the catalyst . the formaldehyde treatment and curing may take place in the same treating chamber or in separate chambers or zones of the treating apparatus . it is sometimes desirable , depending upon the desired characteristic of the fabric , to add to the fabric a polymeric resinous additive that is capable of forming a soft film . for example , such additives may be a latex or fine aqueous dispersion of polyethylene , various alkyl acrylate polymers , acrylonitrile - butadiene copolymers , deacetylated ethylene - vinyl acetate copolymers , polyurethanes and the like . such additives are well known to the art and generally commercially available in concentrated aqueous latex form . for use in the process of this invention , such a latex is diluted to provide about 1 % to 3 % polymer solids in the aqueous catalyst - containing padding bath before the fabric is treated therewith . however , it is not necessary or desirable to add monomers or formaldehyde binding agents . as the cellulosic fiber - containing fabric which may be treated by the present process there can be employed various natural or artificial cellulosic fibers and mixtures thereof , such as cotton , linen , hemp , jute , ramie , sisal , rayons , e . g ., regenerated cellulose ( both viscose and cuprammonium ). other fibers which may be used in blends with one or more of the above - mentioned cellulosic fibers are , for example , polyamides ( e . g ., nylons ), polyesters , acrylics ( e . g ., polyacrylonitrile ), polyolefins , polyvinyl chloride , and polyvinylidene chloride . such blends preferably include at least 35 % to 40 % by weight , and most preferably at least 50 % to 60 % by weight , of cotton or natural cellulose fibers . the fabric may be a resinated material but preferably it is unresinated ; it may be knit , woven , non - woven , or otherwise constructed . it may be flat , creased , pleated , hemmed , or shaped prior to contact with the formaldehyde containing atmosphere . after processing , the formed crease - proof fabric will maintain the desired configuration substantially for the life of the article . in addition , the article will have an excellent wash appearance even after repeated washings . the equipment necessary to carry out the process is very much simplified since moisture control is not used as the moderator for the reaction . the aqueous , acid catalyst may be applied by padding or spraying . moisturization of the fabric , if additional moisture is necessary , may be carried out by passing the fabric through a fog of water before entering the reaction chamber . the fabric containing the latent catalyst may then be placed in a reaction chamber to which gaseous formaldehyde is supplied from any convenient source , e . g ., a formaldehyde generator wherein formaldehyde vapor is produced by heating para - formaldehyde . the formaldehyde vapors are diluted with air or other gas to provide the desired concentration . preferably , the formaldehyde is generated outside the chamber containing the fabric to reduce the fire hazard . the reaction chamber is preferably one which can be heated to a sufficiently high temperature to insure that the cross - linking reaction takes place . the atmosphere in the reaction chamber is preferably a mixture containing from 1 % to 6 . 5 % formaldehyde gas by volume , diluted with air or an inert gas such as nitrogen . higher concentrations of formaldehyde could be used but are not required by this process . to contact the fabric with formaldehyde vapors any suitable means may be employed . for example a batch system utilizing a closed vessel or tube containing the gaseous formaldehyde or into which formaldehyde is introduced may be used . the catalyst - containing fabric may be placed in the treating vessel for the appropriate time . in the alternative , a dynamic or continuous system can be used such as one wherein a stream of formaldehyde vapor is passed through a closed elongated chamber through which the fabric is also passed at an appropriate rate , either concurrently or countercurrently relative to the formaldehyde vapor or gas mix . it is also possible to use combinations of the above , such as by passing a stream of formaldehyde containing gas over a stationary fabric . having generally described this invention , a further understanding can be obtained by reference to certain specific examples which are provided herein for purposes of illustration only and are not provided herein for purposes of illustration only and are not intended to be limiting unless otherwise specified . the fabric was a 50 / 50 polyester cotton sheeting which was padded with an aqueous sulfurous acid solution of catalyst as indicated in the following table 1 to provide about 100 % pick - up . the amount of catalyst shown in table 1 is solution concentration , which at 100 % pick - up of solution by the fabric also corresponds to the amount of catalyst by weight incorporated into the fabric based on the dry weight of the fabric . the cellulose fibers of the cloth at the 100 % pick - up of solution were swollen to their maximum extent . the samples , without drying , were then placed in a heating chamber into which vapors from an amount of paraformaldehyde calculated to provide about 3 . 06 % by volume of formaldehyde were introduced . the samples were exposed to the formaldehyde vapors for several minutes at about 100 ° f . and were then heated to about 245 ° f . in the chamber atmosphere . the samples were then removed from the chamber , washed and dried . the crease resistance ( wrinkle recovery ) was determined by a . a . t . c . c . test method 66 - 1968 and the wash appearance ( d . p . wash ) was determined in accordance with a . a . t . c . c . test method 124 - 1969 in which a rating of 5 is most satisfactory . the results are set forth in table 1 . table 1______________________________________sample sulfurous crease recovery angle d . p . no . acid (% so . sub . 2 ) warp filling w + f rating______________________________________1 6 . 23 152 . 3 150 . 7 303 . 0 4 . 02 3 . 12 151 . 0 155 . 7 306 . 7 4 . 03 2 . 08 145 . 0 148 . 7 293 . 7 3 . 04 1 . 56 144 . 0 140 . 3 284 . 3 3 . 05 1 . 25 128 . 3 125 . 7 254 . 0 2 . 06 0 . 62 117 . 7 119 . 3 237 . 0 1 . 5control -- 110 . 0 112 . 7 222 . 7 -- ______________________________________ as can be seen from the table , excellent crease resistance and wash appearance were obtained . a crease resistance of 290 and a wash appearance of 3 is considered good by current standards in the industry .