The high cost of commercial textbooks in higher education creates barriers to equitable access to learning materials and negatively impacts student performance. Open educational resources (OER) offer a cost-effective alternative, but their impact on student learning remains a critical question. This study directly compared student outcomes between OER and commercial textbooks in a controlled reciprocal design. Forty undergraduate participants completed reading tasks and knowledge assessments using both textbook types, focusing on topics in DNA structure and function and population ecology. Results showed no significant differences in learning gains between OER and commercial textbooks, consistent with prior research. However, participants spent significantly less time on task when using the shorter, learning objective-aligned OER readings, particularly for jargon-heavy DNA content. These findings highlight the potential of OER to reduce cognitive load and improve efficiency without compromising learning outcomes. Future research should explore the role of textbook alignment, length, and student preparation strategies in optimizing learning with OER, particularly in flipped classroom contexts. This study supports OER adoption as a cost-saving measure that maintains academic integrity while enhancing accessibility and efficiency.