The present invention relates to biodegradable polyethylene glycol based water-insoluble hydrogels comprising backbone moieties which are interconnected by hydrolytically degradable bonds, the backbone moieties further comprising reactive functional groups, wherein the water-insoluble hydrogel is further characterized in that the ratio between the time period for the complete degradation of the hydrogel by hydrolysis of the degradable bonds into water-soluble degradation products comprising one or more backbone moieties and the time period for the release of the first 10 mol-% of water-soluble degradation products comprising one or more backbone moieties based on the total amount of backbone moieties in the hydrogel is greater than 1 and equal to or less than 2. The invention further relates to conjugates of such hydrogels with ligands or ligating groups, prodrugs and pharmaceutical compositions as well as their use in a medicament.