Types of Interior Window Trim

Updated July 20, 2017

Interior window trim is used to provide a decorative finish for the interior of a window frame, but it also serves the purpose of closing gaps between the window frame and the wall, stopping drafts that may result from a gap. There are different types of window trim available, including wood, plastic, aluminium and plaster. There are various factors to consider when choosing trim, including the interior style of the home, cost, level of maintenance required and how much it may improve the home's efficiency.

Wood Trim

Interior wood trim is also referred to as window casing. While wood trim is not as common as it once was, it can be an attractive option for framing a window. Wood trim can be nailed around the outside of the window and the remaining gaps filled in with caulking. Wood is a natural material that may require the treatment of knots. Wood is versatile in that it can be painted or stained and easily match any colour scheme or decor. Common woods used for interior window trim include oak, maple and walnut.

Cellular PVC Plastic

Cellular PVC plastic trim is filled with tiny air bubbles, making the material more lightweight and less expensive to produce. Many modern window frames currently use this material, as it is very durable and does not discolour in sunlight like other plastic types. It does not rot, is not affected by insect attacks and it is waterproof. PVC plastic can be glued around the window frame to the wall. Some varieties have an embossed wood grain side and a smooth side for those consumers who want a choice. PVC plastic can be fairly expensive -- about the same price as a knot-free wood, according to The Family Handyman website. While it does not require painting, it can absorb paint easily.


Aluminium is normally used for exterior trim, but it can also be used for interior window trim, particularly with aluminium window units. It is very durable and long-lasting and does not require much maintenance. On the downside, it is more difficult to work with, as it needs to be cut with a mitre saw and bent into shape with special tools. Aluminium trim can be nailed into the window frame using aluminium fixing nails and the gaps can be filled with caulking. Aluminium can be painted or left unfinished.


Plaster is a soft and wet substance when it is first mixed. It eventually dries and hardens. For interior window trim, it can either be moulded on-site or pre-moulded and installed. Often used for curved windows or ornate mouldings, it can be used to create attractive historic designs. A common stock moulding design is the clamshell, where the outer edge is higher than the inner edge, with a smooth, curved face.


When considering new interior trim for a window, it is necessary to take into account the architecture of the room and what style you want the room to have. There are very simple styles available, but consumers can also choose custom-made interior window trim, such as specially carved wood trim elements. Window trim should ideally match that of any door frames in the home. While trim can serve to stop drafts from entering the home, make sure that there is proper insulation around the window.

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About the Author

Based in New Hamburg, Ontario, Mary Margaret Peralta has been writing for websites since 2010. She has developed a company website and a health and safety manual for a past employer. Peralta obtained her Bachelor of Arts in sociology from the University of Waterloo in Waterloo, Ontario.