How are open textbooks free?
Open textbooks are free because the authors of the texts volunteered their time, effort, and expertise. They recognized the importance of providing access to educational resources to people who might otherwise not be able to afford them. The volunteer model is actually quite common now with digital media. For example, everyone who edits or creates Wikipedia pages does so with no expectation of deriving any financial gain from their work. Open source software development works much the same way.
