Hello maxschaf,

Thank you for posting in our community.

What I can suggest for achieving your requirement is using conditional templates for the items of the igCombo. Conditional templates allow you to customize the look and feel based on some condition. For example in your scenario, you could use the value of the igCombo elements to mark which of them will be used as group headers and which will be elements.  The value of the element could be checked and if the value is corresponding to a header, a style for headers could be applied and vice versa, if the value is corresponding to an element, a style for elements could be applied. For example:

<script type="text/javascript">
    $(function () {
 
        var cars = [
 
            //elements with value 1 will be used for group headers and elements with value 2 will be used for group items
            {
                "Name": "Ford",
                "Value": 1
               
            },
 
            {
                "Name": "Focus",
                "Value": 2
            },
 
        {
 
            "Name": "Escort",
            "Value": 2
        },
 
         {
 
             "Name": "Opel",
             "Value": 1
        },
        {
            "Name": "Corsa",
            "Value": 2
        },
          {
              "Name": "Astra",
              "Value": 2
          }
 
        ];
 
        $("#comboIG").igCombo({
            dataSource: cars,
          textKey:"Name",
            valueKey: "Value",
           
            width: "270px",
           multiselction: "on",
          
         itemTemplate: "{{if${Value} == 1}} <b>${Name}</b> {{else}} <div class='padding'>${Name}</div> {{/if}}"
        });
 
     
 
    });
</script>

Some further reference about Infragistics Templating Engine could be found at:

http://help.infragistics.com/Help/Doc/jQuery/2012.1/CLR4.0/html/Templates_Overview.html

Please let me know if you need any further assistance with this matter.

1. Log into the Infragistics Product Idea site at http://ideas.infragistics.com (creating a new login if needed).
2. Navigate to the product / platform channel of your choice (e.g. WPF, Windows Forms, ASP.NET, HTML5 / Ignite UI, iOS / NucliOS, etc.)
3. Add your product idea and be sure to be specific and provide as much detail as possible.

• Explain the context in which a feature would be used, why it is needed, why it can’t be accomplished today, and who would benefit from it. You can even add screenshots to build a stronger case. Remember that for your suggestion to be successful, you need other members of the community to vote for it. Be convincing!
• Include a link to this thread in your idea so product management will be able to look back at this case. 

The Product Idea site puts you in the driver’s seat and allows you to track the progress of your ideas at any time, see how many votes it got, read comments from other developers in the community, and see if someone from the product team has additional questions for you.

Thank you for using Infragistics components.