Students with high reading proficiency typically achieve better results in science assessments, indicating the importance of reading proficiency. Since the process of reading is a complex interaction between properties of a text and a reader, the linguistic demands of a text might affect text comprehension. Certain linguistic features, such as complex syntactic structures and low word frequency, have been found to create higher cognitive load. However, studies investigating the influence of linguistic features on test item difficulty and students' text comprehension in science have hitherto let to inconclusive results. The present study investigates whether the linguistic demands of expository text affect German students' text comprehension in the domain of physics. Within an experimental study, we presented three introductory texts on different subtopics of thermodynamics and 27 single-select, multiple-choice items to 812 secondary school students (grades 7-9). Items measured students' text comprehension (dependent variable); the linguistic demands of each text were systematically varied across three levels (independent variables) while other features of text quality and content were held constant. The results of the item response theory analysis indicated no consistent differences in item difficulty across levels of linguistic demands. Moreover, differential analyses of subgroups presented no consistent differences in solution frequencies of items related to different linguistic demands. Furthermore, while the highest linguistic demand of the texts led the students to perceive a lower comprehensibility, their text comprehension was not affected. Hence, this study provides evidence that the influence of linguistic features on text comprehension is at most low and might be overestimated in present discussions.