A gelling composition for forming a transparent fire-resistant hydrogel interlayer within a glazing unit, the gelling composition obtained by mixing together: 5-40% w/w of a curable hydrogel-forming component; one or more salts; and 40-90% w/w of an aqueous vehicle; characterised in that: the composition has a pH between 3 and 6.8; and the one or more salt(s) comprise monovalent or divalent metal cations or a combination thereof and are present within the composition at a concentration of 20-60% w/w; and the curable hydrogel-forming component comprises: a polymerisable hydrophilic monomer selected from the group consisting of acrylic acid, methacrylic acid, itaconic acid, vinylsulfonic acid, allylsulfonic acid, methallylsulfonic acid, styrenesulfonic acid, 2-acrylamide-2-phenylpropanesulfonic acid, 2-acrylamide- 2-methyl-propanesulfonic acid, vinyl phosphoric acid, (meth)acrylate of ethylene oxide-modified phosphoric acid, N,N-dimethylaminoethyl methacrylate, N,N-diethylaminoethyl methacrylate, N.N-dimethylaminoethyl acrylate, N,N-dimethylaminopropylmethacrylamide, N,N-dimethylaminopropylacrylamide; or a polymerisable hydrophilic monomer defined by Formula: wherein R 1 is H, or alkyl; R 2 is selected from OH, OR 3, NH 2, NHR 3, and NR 3 R 4; and R 3 and R 4 are independently alkyl; or a salt thereof. 5-40% w/w of a curable hydrogel-forming component; one or more salts; and 40-90% w/w of an aqueous vehicle; the composition has a pH between 3 and 6.8; and the one or more salt(s) comprise monovalent or divalent metal cations or a combination thereof and are present within the composition at a concentration of 20-60% w/w; and the curable hydrogel-forming component comprises: a polymerisable hydrophilic monomer selected from the group consisting of acrylic acid, methacrylic acid, itaconic acid, vinylsulfonic acid, allylsulfonic acid, methallylsulfonic acid, styrenesulfonic acid, 2-acrylamide-2-phenylpropanesulfonic acid, 2-acrylamide- 2-methyl-propanesulfonic acid, vinyl phosphoric acid, (meth)acrylate of ethylene oxide-modified phosphoric acid, N,N-dimethylaminoethyl methacrylate, N,N-diethylaminoethyl methacrylate, N.N-dimethylaminoethyl acrylate, N,N-dimethylaminopropylmethacrylamide, N,N-dimethylaminopropylacrylamide; or a polymerisable hydrophilic monomer defined by Formula: wherein R 1 is H, or alkyl; R 2 is selected from OH, OR 3, NH 2, NHR 3, and NR 3 R 4; and R 3 and R 4 are independently alkyl; a polymerisable hydrophilic monomer selected from the group consisting of acrylic acid, methacrylic acid, itaconic acid, vinylsulfonic acid, allylsulfonic acid, methallylsulfonic acid, styrenesulfonic acid, 2-acrylamide-2-phenylpropanesulfonic acid, 2-acrylamide- 2-methyl-propanesulfonic acid, vinyl phosphoric acid, (meth)acrylate of ethylene oxide-modified phosphoric acid, N,N-dimethylaminoethyl methacrylate, N,N-diethylaminoethyl methacrylate, N.N-dimethylaminoethyl acrylate, N,N-dimethylaminopropylmethacrylamide, N,N-dimethylaminopropylacrylamide; or a polymerisable hydrophilic monomer defined by Formula: wherein R 1 is H, or alkyl; R 2 is selected from OH, OR 3, NH 2, NHR 3, and NR 3 R 4; and R 3 and R 4 are independently alkyl; wherein R 1 is H, or alkyl; R 2 is selected from OH, OR 3, NH 2, NHR 3, and NR 3 R 4; and R 3 and R 4 are independently alkyl; or a salt thereof.