You can apply conditional formatting to customize the appearance of data bars in Excel for a more informative visual representation of your data. Here's how:

1. Select your data range:
- Highlight the cells containing the numerical values you want to represent with data bars.

2. Apply Conditional Formatting:
- Go to the "Home" tab on the Excel ribbon.
- In the "Styles" group, click the dropdown arrow next to "Conditional Formatting."

3. Choose Data Bars:
- Several options will appear. Hover over "Data Bars" to reveal a submenu.
- You can choose from "Gradient Fill" or "Solid Fill" for data bars. Gradient Fill transitions colors based on data values, while Solid Fill uses a single color.

4. Edit Formatting Rules (Optional):
- By default, Excel applies a generic data bar format. To customize it further:
- Click on "More Rules..." at the bottom of the "Data Bars" submenu.
- This opens the "New Formatting Rule" window.

5. Set Up Data Bar Rules:
- Under "Select a Rule Type," choose "Format all cells based on their values."
- Here, you can define how data bar appearance changes based on your data:
- Minimum and Maximum: Set the minimum and maximum values for your data range. Data bars will grow longer as values approach the maximum and shorter for values closer to the minimum.
- Bar Color: Click on "Bar Color" to choose the color gradient or solid color for your data bars.
- You can also set formatting for negative values by clicking the "Negative Value/Axis" button and customizing their appearance.

6. Apply the Formatting:
- Once you've set up your desired data bar formatting, click "OK" to apply the rule to your selected data range.

Additional Tips:

* You can further customize data bars by formatting the axis (the line alongside the bar) and data bar border through the "New Formatting Rule" window.
* Conditional formatting allows for more advanced data bar customization using formulas. This lets you define specific conditions for data bar appearance based on calculations.

By applying conditional formatting to data bars, you can create a visually appealing and informative representation of your data, making it easier to identify trends and patterns within your spreadsheet.