Antifouling additive comprising a. an inorganic, silica-containing aerogel comprising b. a porous gel lattice with i. a total porosity of at least 40%, and ii. a mesopore diameter of at least 10 nm, c. optionally an alcoxide comprising Sc, Ti, V, Cr, Mn, Fe, Co, Y, Zr, Nb, Ru, Hf, Ta, W, Re, Al, Ge, In, La, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb or Lu, and d. at least 55% by weight of one or more biocidal or biorepellant compounds selected from 4,5-Dichloro-2-octyl-4-isothiazolin-3-one (DCOIT), 2-(p-chlorophenyl)-3-cyano- 4-bromo-5-trifluoromethyl pyrrole (Econea), Zinc ethylenebisthiocarbamate (Zineb), 3-(3,4-Dichlorophenyl)-1,1-dimethylurea (Diuron), 3-iodo-2-propynylbutylcarbamate (IPBC), 2-tert-butylamino-4-ethylamino-6-methyl-thio-1,3,5-triazine (Terbutryn), 1-(4-chlorophenyl)-4,4-dimethyl-3-(1H-1,2,4-triazol-1-ylmethyl) pentan-3-ol (Tebuconazole), Zinc pyrithione, Tolylfluanid, Dichlofluanid, N,N-Didecyl-N,N-dimethylammonium Carbonate, N,N-Didecyl-N,N-dimethylammonium Bicarbonate, 2-thiazol-4-yl- 1H-benzoimidazole (Thiabendazole), 4-[1-(2,3-Dimethylphenyl)ethyl]-3H-imidazole (Medetomidine), and mixtures thereof entrapped in said aerogel, wherein the entrapment of said one or more biocidal or biorepellant compounds takes place during the SOL-GEL formation of the gel and wherein the SOL-GEL precursor is one or more alkoxysilanes selected from tetraethoxysilane, tetra-n-propoxysilane and alkyltrialkoxysilanes, and wherein the inorganic, silica-containing aerogel contains alkoxysilane (Si-OR) terminal groups selected from ethoxysilane (Si-OEt) or n-propoxysilane (Si-OPr) groups. a. an inorganic, silica-containing aerogel comprising b. a porous gel lattice with i. a total porosity of at least 40%, and ii. a mesopore diameter of at least 10 nm, i. a total porosity of at least 40%, and ii. a mesopore diameter of at least 10 nm, c. optionally an alcoxide comprising Sc, Ti, V, Cr, Mn, Fe, Co, Y, Zr, Nb, Ru, Hf, Ta, W, Re, Al, Ge, In, La, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb or Lu, and d. at least 55% by weight of one or more biocidal or biorepellant compounds selected from 4,5-Dichloro-2-octyl-4-isothiazolin-3-one (DCOIT), 2-(p-chlorophenyl)-3-cyano- 4-bromo-5-trifluoromethyl pyrrole (Econea), Zinc ethylenebisthiocarbamate (Zineb), 3-(3,4-Dichlorophenyl)-1,1-dimethylurea (Diuron), 3-iodo-2-propynylbutylcarbamate (IPBC), 2-tert-butylamino-4-ethylamino-6-methyl-thio-1,3,5-triazine (Terbutryn), 1-(4-chlorophenyl)-4,4-dimethyl-3-(1H-1,2,4-triazol-1-ylmethyl) pentan-3-ol (Tebuconazole), Zinc pyrithione, Tolylfluanid, Dichlofluanid, N,N-Didecyl-N,N-dimethylammonium Carbonate, N,N-Didecyl-N,N-dimethylammonium Bicarbonate, 2-thiazol-4-yl- 1H-benzoimidazole (Thiabendazole), 4-[1-(2,3-Dimethylphenyl)ethyl]-3H-imidazole (Medetomidine), and mixtures thereof entrapped in said aerogel, wherein the entrapment of said one or more biocidal or biorepellant compounds takes place during the SOL-GEL formation of the gel and wherein the SOL-GEL precursor is one or more alkoxysilanes selected from tetraethoxysilane, tetra-n-propoxysilane and alkyltrialkoxysilanes, and wherein the inorganic, silica-containing aerogel contains alkoxysilane (Si-OR) terminal groups selected from ethoxysilane (Si-OEt) or n-propoxysilane (Si-OPr) groups. <EOS>