Best curtains to keep heat out

An exterior knitted shade, rated by the manufacturer at up to 90% UV block, mounted outside the glass on a soffit, beam or pergola. It stops the radiation before it enters, which is the only approach that prevents the heat rather than managing it.

Who it’s for: Patio doors, covered porches and any window with something overhead to mount from. The single most effective option on this page.

The catch: It needs somewhere outdoors to fix to, which rules it out on a bare wall with no overhang. It also has to be rolled up in high wind.

A silver-tone thermal coating facing the glass reflects solar radiation back out before the fabric absorbs it. This is the mechanism that separates a genuinely heat-rejecting curtain from a merely heavy one.

Who it’s for: West and south-facing rooms without an exterior mounting option — the common case.

The catch: It still works after the light is through the glass, so it cannot match an exterior shade. And the coating restricts washing and eventually cracks.

Solar-screen fabric is woven specifically to reject a share of solar energy while you can still see out of it. For a window with a view that you do not want to lose to a wall of blackout fabric, this is the right compromise.

Who it’s for: Living rooms and home offices where the window is hot in the afternoon and the view matters the rest of the time.

The catch: An open weave by definition lets some radiation through, so it reduces heat rather than stopping it. A tighter, darker screen rejects more and shows less view.

The air pockets work in both directions: they slow heat entering in July and slow heat leaving in January. For a room that is a problem at both ends of the year, one product covers both cases.

Who it’s for: Rooms that are too hot in summer and too cold in winter — which is most rooms with a large window.

The catch: Opaque when lowered, so summer comfort means losing the window during the hours you would most like to be looking out of it.

Film applied to the glass itself rejects a share of solar energy at the pane, without any bracket, rail or fabric. It also gives permanent privacy, which on a bathroom or stairwell window is a useful two-for-one.

Who it’s for: Rentals, awkward windows, and rooms where you do not want any hardware at all.

The catch: The heat rejection is modest compared with an exterior shade, and it is permanent — you cannot take it off for the winter, when you might actually want the solar gain.