Astragal vs. T-Post: Which option is best for your customer?

Helping your customer select the optimal finish-out elements for their shutters can be the difference between a happy customer, or an unhappy one. In addition to installation type, color, and tilt rods, they will also want to decide between an Astragal or T-Post.

An Astragal (or D-Mould) is a piece of molding that is added to the stile of a specified panel. It is 1/2” in depth and overlaps the top/front of the adjoining panel.

A T-Post is a stand-alone post that is added to a larger frame to provide additional support. The wider portion of the post is 2 3/16” and is installed on the window side of the opening. The panels will sit on a ⅝” lip with a 1” post separating the panels on the room side.

But which option is right for your customers? To answer this, let’s first look at the benefits and restrictions of both options.


The most important benefit of the astragal is the near blackout* light-blocking feature between 2 panels. It also provides a smoother aesthetic transition between the two panels. However, the astragal comes with panel size limitations. The largest size a panel can be is 41 1/4” wide. If the opening is larger than 82 1/2” total, a T-Post is required, in which case an astragal is typically not used.


The T-Post provides a solution for larger opening sizes and multiple panel configuration options. All openings wider than 83” will require a T-Post, both to support the frame as well as offer a hinged side for the additional panel needed to cover the opening. The T-Post is also often used the cover a mullion (the aluminum strip on a window that separates or creates a division in large glass panels) to aesthetically match the window when the shutters are completely open. One downside to a T-Post is known as the light halo effect. More light bleed* is seen with a T-Post as opposed to an astragal, especially with west-facing windows that receive afternoon sunlight.

*It is important to note that all shutter installations will have some level of light bleed. If the customer wishes a complete blackout window covering, we recommend pairing a blackout shade with the shutter. Sunlight is crafty like that.

But really, which option is best for your customers?

The first question is one of functionality: Is a T-Post needed to support the configuration of the panels, or size of the opening? If the answer is yes, you need look no further. If the answer is no, the next question is, which aesthetic best matches the customer’s desires?

Good luck out there, and happy selling.

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