This article discusses the use and problems of heat-set tissue for dry mending tears and lacunae in paper. Blocking, the unwarranted adhesion between layers by moderate pressure (eg. during storage) may result in damage. Uncontrolled temperature and relative humidity (Rh) affect blocking. The use of anti-blocking mediums (eg. microcrystalline wax, rice starch paste, and calcium or magnesium carbonate) are ineffective during high Rh. A study was undertaken to find a resin which has good aging properties, is lightfast, reversible, stays hard at normal temperatures and Rh, and which forms a continuous film at room temperature. Residual adhesive may result in future blocking, affect appearance and interfere with future treatments. Plasticizing materials are unstable. Compatibility, clarity, yellowness, ph and residual tack were considered. Sixteen polyvinyl acetate and five acrylic resins were tested. Acrylic resin dispersions are recommended in the preparation of heat-set tissue as follows: 1 part Plextol B-500; 1+ parts Rhoplex C-73, 1 part distilled water. References date from 1951 to 1970. A technical article, Heat-Set Tissue Preparation and Application, Library of Congress Publication of Library Materials, Series 300, No. 1 is attached. These articles are references for the conservation treatment of archival and library materials on paper. -- CCI