1. Grid System: One of the key differences between Bootstrap and Pure is their grid system. Bootstrap utilizes a 12-column grid system, allowing for flexible and responsive layouts. On the other hand, Pure adopts a more minimalistic approach with a 5-column grid system, which can be limiting in terms of design flexibility.

2. Component Library: Bootstrap offers a vast collection of pre-built components such as navbars, cards, modals, and more. These components are ready to use and can be easily customized. In contrast, Pure provides a smaller set of basic components, focusing on simplicity and lightweight code. This means that Pure might require more custom development for advanced or specific features.

3. Styling: Bootstrap comes with a predefined and consistent set of design styles, ensuring a cohesive look and feel across different elements. Additionally, Bootstrap offers a wide range of customizable themes and templates. Pure, on the other hand, provides minimal styling for a clean and neutral appearance, allowing designers more freedom to create their own unique styles.

4. JavaScript Dependence: Bootstrap relies heavily on JavaScript for various interactive components and functionality, making it a powerful framework. Pure, in contrast, aims to be lightweight and does not rely on JavaScript for any of its core functionality. This can be advantageous for performance-focused projects or situations where JavaScript is not desired or available.

5. Browser Support: Bootstrap has extensive browser support, including older versions of Internet Explorer. This makes it a suitable choice for projects that require compatibility with a wide range of browsers. Pure also has good browser support, but it may not support older browsers as comprehensively as Bootstrap does.

6. Customization: Bootstrap provides a robust set of customization options, allowing developers to tailor the framework to their specific needs. This includes the ability to choose which components, styles, and JavaScript plugins to include, resulting in a more optimized and streamlined codebase. Pure, while offering some customization options, may be less flexible in comparison.

In summary, Bootstrap offers a more comprehensive and feature-rich framework with a larger component library, extensive customization options, and a powerful grid system, while Pure focuses on simplicity, lightweight code, and minimal styling, making it a suitable choice for more minimalist and performance-focused projects.