Paper card sorting uses traditional paper index cards or sticky notes that users can organize in any way they like. Users don't need to learn how to use a new tool — they just group items into piles and name categories.

• The pros: It's much easier to experiment with physical cards, move them around, or start over the whole process.
• The cons: Researchers must manually create cards and record each participant's groups into a tool for analysis.

Digital card sorting implies using an online tool where the participants use digital cards and drag & drop them into categories.

• The pros: The software collects and analyzes all the data. Researchers can gain insights directly from these findings.
• The cons: Online tools are less flexible and require time to learn. Plus, technical or usability issues can confuse users and prevent them from creating new categories or moving cards between groups.