(CNN) -- College student Caitlin Ryen works two jobs to support herself and pay tuition at South Florida Community College. When a new semester rolls around, that usually means choosing which textbooks to buy, or not buying any at all, she says.
The 22-year-old caught a break this term when she found out her physics course materials were free. Instead of asking students to buy a textbook from a major publishing company, Ryen's professor assigned a free digital textbook that he customized for the class.
Ryen's professor, Erik Christensen, began exploring the format in 2007, when a student asked to borrow a textbook because he couldn't afford one. While looking around for affordable alternatives, Christensen came across the concept of open-source textbooks, or course materials offered for free online by their authors under a nonrestrictive license.
This year, it saved Ryen from having to decide which books to buy, and enabled her to spend $230 on biology course materials, she says. It makes other parts of her life easier, too: She can read her physics textbook on her smartphone before her bartending shift or between classes.
"I think it's great. I use it whenever I can find time to study," she said. "It helps in those moments when you have a little bit of extra time in a place where you wouldn't normally bring a bulky textbook."
Open textbooks are catching on among educators and institutions looking to save students money. A 2014 study by The Student Public Interest Research Groups, which advocates for open textbooks, found that textbook costs are deterring students from purchasing assigned materials and impacting their course selection -- and schools are starting to take notice.
Then why aren't open textbooks more common? Many educators say they are content with proprietary textbooks and don't want to alter their class syllabus for a new text -- a time-consuming task.
Others believe open textbooks don't face the same academic or editorial scrutiny as proprietary texts, which is true with some versions. The nonprofit College Open Textbooks, which promotes awareness and adoption of open textbooks, said in a 2012 report that "copy editing is an issue" with many open texts, noting that "if [they] were to have the same editing quality as proprietary textbooks, they would proliferate faster."
It raises the question of which is better for students: an imperfect textbook or no textbook at all?
To address this concern, publishers of open textbooks are beefing up academic oversight to offer peer-reviewed material that they say is comparable to proprietary textbooks. And, they're finding an audience.
The biggest group of adopters of online education resources are community colleges, where the estimated average $1,200 spent per semester on books and supplies represents a bigger chunk of a student's overall education expenses, experts say.
As the quality of resources improves and technology makes it easier to adopt, bigger state schools and private institutions are getting on board.
Creating a 'living textbook'
Born of the open-source movement that gained steam in the 1990s, the first decade of open textbooks was focused on creating content and getting it online under a Creative Commons license, which meant anyone could access it. Platforms such as MIT's OpenCourseWare, California's MERLOT system, Flat World Knowledge and Rice University's Connexions emerged to offer lesson plans and course materials created by faculty. Under the open license, anyone could take the material and modify it to suit their needs.
Now that the material is out there, the focus has shifted to encouraging schools to adopt it, said Wiley, who left a tenured teaching post at Brigham Young University to do just that. His company, Lumen Learning, helped Tidewater Community College in Virginia develop a "textbook-free" pilot for its associate's degree in business administration, which launched in September.
Some teachers are building their own texts from scratch based on existing online education resources, articles and videos available on the web. But, the most commonly used open textbooks are developed by organizations acting as digital publishers, such as OpenStax, a nonprofit that grew out of Connexions in 2012; it's used by teachers at 500 institutions, including South Florida Community College.
OpenStax is funded by grants, which allow it to offer digital books that students can download and print for free. They also have the option of requesting a hardcopy, the price of which ranges from $30 to $50 depending on the course, or an iBooks version for $4.99.
"We've created a book that can be continuously updated for errors and changing events in the world," OpenStax creator Richard Baraniuk said. "How many times would we have to rewrite the chapter on modern Egypt? That situation is almost changing daily, so this dream of getting toward a book that's truly a living textbook is nearly at hand."
The texts can be more flexible than the bound books students used to lug around, too. Christensen, the South Florida Community College physics teacher, said he modified the OpenStax textbook his classes use to add more calculus and include location and city names more familiar to his Central Florida students. He can also fix typos and errors on the spot instead of waiting for a publisher to issue a new edition.
"I wanted to expand access to the course and affordability is a part of that," Christensen said. "But I also want to make sure it's a quality product."
Other platforms, like the Boston-based company Boundless, also offer customizable, intro-level textbooks in more than 20 subjects. When Boundless launched in 2010, students made up its biggest group of early adopters, CEO Ariel Diaz said. Teachers followed close behind, adopting Boundless' books as course materials. Now, the company offers a "premium package" to students for $19.99 that includes flashcards, slides for building presentations, homework and classroom management tools.
Traditional textbook publishing companies defend their products and prices, saying they offer unparalleled levels of academic and editorial oversight. Plus, they have taken steps to lower prices in recent years by offering rental and buyback programs, along with making digital versions available.
But proponents of open textbooks say they offer comparable, peer-reviewed material. Besides, traditional course materials also have been known to contain errors, said C. Edward Watson, director of the Center for Teaching and Learning at the University of Georgia. For the first time this year, the university introduced an OpenStax biology textbook as part of an online educational resource initiative. It saved more than $100 for more than 2,000 students.
"Our faculty says the imperfect free textbook is better than the imperfect expensive textbook," Watson said. There's a lot of things students can't do without -- tuition, fees, rent -- so students are choosing not to purchase books, and it hurts them in the long run."
'I wish all professors used this format'
Most schools are far from eliminating paper books on campus, but open-textbook use is picking up in high-enrollment introductory courses. That's where savings and flexibility can have the greatest impact, experts say.
With about 700 enrolled students paying at least $100 a year on course materials for his introductory psychology class, University of Maryland instructor Scott P. Roberts saw an opportunity to save big, especially as textbook costs continued to rise with each new edition.
"There's very little the updates are adding most of the time that justifies such a higher cost," he said. "That frustration really got me thinking about why we were asking students to pay for access to information that really is available already online."
Instead of adopting someone else's open textbook, he decided to make his own using articles, studies and videos available for free online under a Creative Commons license. Any content he couldn't find, he wrote himself. He compiled them into a Word document that he distributed as an interactive PDF with videos and links.
He migrated to a blog platform the following year, which allows him and colleague Ryan Curtis to update faster if a new study or TED Talk comes out. When the new version of the Diagnostic Statistical Manual was released in 2013, they were able to edit the chapter within a week to reflect new categories.
He harbors no illusions of putting the textbook publishers out of business, but for many students "this levels the playing field," he said. Before, he saw that even students who struggled academically were putting off textbook purchases.
"This removes major barrier to access for students who already are at a greater risk for underperforming," he said.
By the time senior Josh Stonko joined Roberts' class this year, he was already familiar with open textbooks. Earlier, his economics professor co-authored course materials with other professors and made them available online as a downloadable PDF.
"I wish all the professors used this format," Stonko said. "It makes much more sense for students who are struggling financially, which is a large percentage of the student body."
Stanko likes learning this way, too. Diagrams and charts in the book matched those used in lectures, reinforcing ideas in a seamless manner.
"It makes the transition from assignment to class smoother," he said.
Several University of Maryland professors are experimenting with open textbooks, said Ben Bederson, executive director of the university's new Teaching and Learning Transformation Center.
He dismisses criticism that open educational resources diminish the quality of education or threaten classroom attendance more than regular textbooks. If anything, easy online access to information is good for students and faculty because it places a premium on classroom interactions.
"I think our classes are getting better and better because we have a better understanding of pedagogy and stronger motivation because of free alternatives," he said."I do think it requires some shifting as we think about how we make better use of face-to-face courses."
Bederson, a computer science professor who previously led Maryland's Human-Computer Interaction Lab, says that evaluating open textbooks is high on his list of priorities. Educators switching to open textbooks at Maryland aren't part of an organized university initiative -- at least, not yet.
"As we develop a better understanding of what makes nonpaid resources work well, then we can start to encourage it more and more," he said.