Square-Hole vs Round-Hole Security Screen Mesh: Airflow, Light, Insects and Security

What are square-hole and round-hole security mesh?

Security screen mesh is a heavy plain-weave stainless steel mesh, usually 11 mesh with 0.8 mm wire, finished with polyester powder coating. In a plain weave the wires cross at right angles, so the bare mesh always has square openings. Whether the finished mesh shows square or round holes depends on how it is coated.

• Square holes: a thin, even powder coat follows the round wire. The corners of each opening stay open, so the holes remain square.
• Round holes: a different powder is applied in a larger quantity. The extra powder collects where the wires cross and fills the four corners of each opening, leaving a round hole.

Both finishes are applied in a single coat, and the manufacturer chooses which one to produce. You can tell them apart by eye: hold a sample up to the light.

Round holes came first. Heavy-wire security mesh was traditionally supplied with round holes; square-hole finishes on heavy wire have only appeared in recent years. Today both are available, and we produce either finish to the customer’s specification.

Why round holes let through less light and air

Hole shape is a matter of simple geometry. A circle drawn inside a square covers π/4 of the square’s area, about 78.5%. When powder fills the four corners of an opening, about 21.5% of that opening is closed.

The width across the opening does not change. A round hole has the same diameter as the side of the square hole it replaces. Only the corners are lost.

Open area by wire diameter

Open area is the share of the screen you can see through. It mostly decides how much light and air the screen lets in. The table shows 11 mesh (2.31 mm wire spacing) in the three most common wire diameters.

Wire diameter	Bare mesh: opening / open area	Square holes: opening / open area	Round holes: opening / open area
0.8 mm	1.51 mm / 43%	≈ 1.41 mm / ≈ 37%	Ø ≈ 1.41 mm / ≈ 29%
0.9 mm	1.41 mm / 37%	≈ 1.31 mm / ≈ 32%	Ø ≈ 1.31 mm / ≈ 25%
1.0 mm	1.31 mm / 32%	≈ 1.21 mm / ≈ 27%	Ø ≈ 1.21 mm / ≈ 22%

How these figures are calculated: wire spacing = 25.4 mm ÷ 11. Opening = wire spacing − coated wire diameter. Square open area = (opening ÷ wire spacing)². Round open area = square open area × π/4. Coated figures assume about 0.05 mm of powder on each side of the wire. Real coatings vary, so treat the coated values as close estimates.

Two points stand out. Going from 0.8 mm to 1.0 mm wire costs about 10 points of open area. Choosing round holes instead of square costs about 6–8 points on each wire size. A 0.8 mm round-hole mesh lets through less light than a 0.9 mm square-hole mesh.

Airflow, light, insects and security compared

	Square holes	Round holes
Light	More light; about 37% open area on 0.8 mm wire	About 21% less light than square holes on the same mesh
View through the screen	Clearer view; the wires look thinner	Darker; the solid area around each hole is larger
Airflow	Better ventilation	Lower; less open area means more resistance to air
Insects	Same narrowest gap as round holes	Same narrowest gap; the larger diagonal gap of a square hole is closed
Cut and impact resistance	Set by wire diameter, stainless steel grade and the screen system	Same; the steel wire is identical
Appearance	Fine, regular square grid	Rows of round holes, similar to a perforated sheet

Light and view. Open area is roughly the share of light that passes straight through, so round holes make the screen noticeably darker. The extra solid area at each wire crossing also makes the mesh more visible from inside, which matters for windows with a view.

Airflow. Air passes through the openings, so a smaller open area gives more resistance and less ventilation at the same wind pressure. If ventilation is the main reason for the screen, square holes are the better choice.

Insects. Whether an insect gets through depends on the narrowest gap. A round hole is as wide as the square hole it replaces, so both finishes stop the same insects. Round holes close only the diagonal of the square, which is about 1.4 times the side. In practice, mesh count and wire diameter matter far more for insect protection than hole shape.

Security. The stainless steel wire inside the coating is the same in both finishes. Cut and impact resistance come from the wire diameter, the grade (304 or 316) and the weave. Hole shape does not make the mesh stronger or weaker.

In Australia, security door and window screens are assessed as complete products under the AS 5039 series: AS 5039.1:2023 sets the performance requirements, AS 5039.3:2023 sets the test methods (impact, jemmy, pull, probe and knife shear) and AS 5039.2:2024 covers installation. These parts replace the older AS 5039-2008, AS 5041-2003 and AS 5040-2003. Testing applies to the finished screen, including the frame, the way the mesh is held in it and the locks, not to the mesh on its own.

How to tell square holes from round holes

• Hold the mesh up to the light. Square holes show a regular square grid; round holes show rows of round dots of light. The difference is clear to the eye.
• Compare samples side by side. For the same wire diameter, the round-hole sample looks darker overall.
• Ask for the finish in writing. State “square hole” or “round hole” on the order and approve a sample before production. Both are produced to order, so the finish should never be a surprise.

Which one should you choose?

Choose square holes when light, a clear view or ventilation matters most: windows, balconies and patios, and markets where a “see-through” screen is the selling point.

Choose round holes when your market is used to the traditional round-hole look, or your customers prefer it and accept a darker screen with less airflow.

Choose a heavier wire, not a heavier coat, when you need more strength. 0.9 or 1.0 mm wire with square holes adds steel while keeping more open area than 0.8 mm wire with round holes.

What to include in your enquiry

• Stainless steel grade: 304 or 316 (316 for coastal areas and around pools)
• Mesh count and wire diameter, e.g. 11 mesh × 0.8 mm
• Hole finish: square hole or round hole
• Colour: black, grey or white
• Roll width (0.6–1.5 m) and length (31.5 m standard), or cut sheet sizes
• Quantity and destination port
• Whether you need a sample before production