Cloudhadoop - mat-expansion panel

Angular Material's expansion panel is one of the most versatile components for managing vertical space. Before we dive into the template syntax, we must ensure our Angular 17+ or 18+ project is correctly configured to use the Material library.

Module configuration and setup

In modern Angular applications, you'll typically be using standalone components. To use the expansion panel, you need to import MatExpansionModule in your component's imports array. If you are still using the traditional module-based architecture, add it to your app.module.ts.

import { MatExpansionModule } from '@angular/material/expansion';

@Component({
  selector: 'app-my-tutorial',
  standalone: true,
  imports: [MatExpansionModule],
  templateUrl: './my-tutorial.component.html'
})
export class MyTutorialComponent { }

Static vs Dynamic content rendering

One of the critical decisions developers face is whether to render content eagerly (static) or lazily (dynamic). The mat-expansion-panel provides a specialized directive called matExpansionPanelContent to defer the rendering of the panel's body until it is actually expanded.

This is particularly important for performance when you have complex child components or heavy data fetching within your panels. By utilizing lazy rendering, you reduce initial load time and memory usage.

The basic structure of an expansion panel consists of three main elements: mat-expansion-panel (the container), mat-expansion-panel-header (the clickable part), and the content area.

<mat-expansion-panel>
  <mat-expansion-panel-header>
    <mat-panel-title> Personal Details </mat-panel-title>
    <mat-panel-description> Type your name and age </mat-panel-description>
  </mat-expansion-panel-header>

  <p>This is the body of the expansion panel.</p>
</mat-expansion-panel>

Note how the mat-panel-title and mat-panel-description work together to create a professional look. In 2026, accessibility is paramount; these components handle ARIA attributes automatically, ensuring your collapsible sections are readable by screen readers.

Expansion panels aren't just for text. They are frequently used to hold complex lists, form controls, or even nested accordions. By combining mat-list with the panel, you can create hierarchical navigation menus or detailed property inspectors.

Expert Tip: Use mat-accordion around multiple panels to ensure only one section is open at a time (multi="false").

<mat-accordion>
  <mat-expansion-panel hideToggle>
    <mat-expansion-panel-header>
      <mat-panel-title> Advanced Settings </mat-panel-title>
    </mat-expansion-panel-header>
    <mat-list>
       <mat-list-item> Network Configuration </mat-list-item>
       <mat-list-item> Security Protocols </mat-list-item>
    </mat-list>
  </mat-expansion-panel>
</mat-accordion>

In real-world applications, your panels are rarely static. You often need to generate them from an API response or a structured data source.

When dealing with complex data structures, such as a typescript dictionary, iterating through keys and displaying values becomes a standard pattern.

<mat-accordion>
  <mat-expansion-panel *ngFor="let item of items">
    <mat-expansion-panel-header>
      <mat-panel-title> {{ item.label }} </mat-panel-title>
    </mat-expansion-panel-header>
    <div> {{ item.content }} </div>
  </mat-expansion-panel>
</mat-accordion>

State management is where you unlock the true power of Angular Material. You can control the visibility of a panel using the [expanded] input property or by using ViewChild to call the open(), close(), and toggle() methods programmatically.

If you are building a complex UI that uses icons from the primeng icons list, you can easily integrate them into the mat-expansion-panel-header to provide better visual cues to your users.