Attractive materials that absorb large quantities of water are called hydrogels. They have interesting properties which can be easily shown with experiments and combined with explanation of certain science concepts and phenomena. Hydrogels are spread in food, pharmaceutical and agriculture industry. The informal conversations with students show that they are not aware of their existence. Hydrogels can be easily included into teaching of physics in chemistry in high schools, therefore we decided to explore students' conceptions about hydrogels after the high school. 104 pre-service primary school teachers from Faculty of Education, University of Ljubljana, were included into the study. Students filled in a paper-pencil questionnaire with 26 items on February 2015 at the beginning of the spring semester. Students achieved 0.8 points out of 10 on items testing the knowledge about hydrogels. This shows on limited knowledge about hydrogels. Results present the starting point for the designing of the teaching module about hydrogels.