A window casing is the trim that frames a window opening — the head casing across the top, the side casings down each sides, and sometimes a small stool (the horizontal trim at the bottom of the window, inside the casing) and an apron (the trim below the stool). The casing frames the window, covers the gap between the window frame and the wall, and provides the visual transition between the wall and the window.
A PU window casing is a complete trim kit, factory-made from the same material and finish, designed to frame a standard window. The casing includes the head casing, the side casings, and sometimes the stool and apron. The pieces are pre-cut to standard window sizes, with miters at the corners and pre-finished surfaces.
The advantage of PU window casings is the speed of install. A window that would take a carpenter half a day to frame with raw wood or MDF trim can be framed with a PU casing in one to two hours. The pieces are pre-cut, the joints are pre-mitered, and the finish is pre-primed.
The aesthetic range covers the full design vocabulary. A modern casing is a simple rectangular profile, painted the same color as the wall. A traditional casing has a more developed profile (a stepped casing, a small cornice, optional plinth blocks at the base). A formal casing has a small pediment above the head casing, with classical details.
For sourcing, PU window casings are a stock product at most factories. The casings are available in a range of standard sizes (to fit standard window dimensions), a range of standard designs (modern, traditional, formal), and a range of standard finishes. Custom sizes are available on longer lead times.
A practical install note: the window casing is installed after the window and the window frame are in place. The side casings are installed first, plumb on each side of the window. The head casing is installed next, level across the top of the side casings. The stool (if any) is installed third, across the bottom of the side casings. The apron (if any) is installed last, below the stool. The joints are filled with paintable caulk, and the painter's topcoat goes on the next day.
A practical note on the stool and apron. The stool is the horizontal trim at the bottom of the window, inside the casing. The apron is the trim below the stool, applied to the wall. The stool provides a small ledge at the bottom of the window (useful for plants or objects), and the apron provides a visual base for the window. Both are traditional details, often omitted in modern interiors.
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Frequently Asked Questions
Q: What is polyurethane (PU) decorative material?
A: Polyurethane (PU) decorative material is a high-density closed-cell polymer molded into architectural profiles such as cornices, ceiling medallions, wall panels, columns, and skirting boards. It replicates the appearance of plaster, carved wood, or stone at one-quarter the weight, is fully waterproof, impact-resistant, and arrives factory-primed for paint.
Q: How does PU compare with plaster and wood mouldings?
A: PU is lighter than plaster (no scaffolding required), impact-resistant during transport, and immune to cracking. Compared with wood, PU does not warp, split, or attract termites, and it tolerates moisture in bathrooms and kitchens. The trade-off: PU cannot be refinished the way solid wood can, but its lifespan is 20–30+ years with minimal maintenance.
Q: How do you cut and finish PU mouldings?
A: Cut PU mouldings with a fine-tooth miter saw (40+ teeth for a 10-inch blade) to avoid chipping the molded edge. Sand the cut edge with 220-grit, then apply two coats of interior latex paint. Mitre joints at corners, fill seams with lightweight spackle, sand smooth, and finish with one final top coat.
Q: Is PU moulding safe for indoor air quality?
A: Yes. Premium PU mouldings are manufactured without formaldehyde, asbestos, or VOCs. They meet EN 13501-1 Class E fire classification as a minimum, with Class B fire-retardant versions available for commercial projects. The factory-applied water-based primer further reduces off-gassing once installed.