No-See-Um Mesh vs Standard Pool Screen: What You Trade

Most pool cages in Florida wear one of two fiberglass meshes: 18x14 pool and patio screen or 20x20 no-see-um screen. The choice looks like a question about bugs. It is also a question about view, breeze and how much wind load the frame was designed to carry.

What do 18x14 and 20x20 mean on a pool screen?

Mesh count is the number of yarns woven in each direction. Phifer, a screen manufacturer, defines the two numbers as how many yarns run vertically by how many run horizontally within a square inch of screen. An 18x14 mesh has 18 one way and 14 the other; a 20x20 mesh has 20 both ways.

Phifer lists its 18x14 Pool & Patio Screen at a .013-inch yarn diameter and describes it as designed for applications where extra strength is needed to span large openings. Phifer describes its 20x20 No-See-Um Screen as a tightly woven mesh designed to keep out most of the smallest flying insects, including no-see-ums, gnats and sand flies. Phifer’s bug protection page says its no-see-um weave is 15 to 20 percent tighter than standard insect screening.

Which pool screen keeps out no-see-ums?

No-see-um screen keeps out biting midges; standard pool screen is not sold as doing so. UF/IFAS Extension’s profile of biting midges, the insects Floridians call no-see-ums, says adults usually measure 1.0 to 2.0 mm long. The same publication says regular window screens do not exclude biting midges, while the openings of no-see-um screen are small enough to keep them out.

Phifer’s Screen Selection Guide says the same thing in its own terms. It rates the 18x14 mesh Good for insect protection and the 20x20 No-See-Um screen Best. Phifer’s 18x14 product page promises to keep out most insects, while its no-see-um page names the smallest ones.

Pool Pros Construction projects include the finer mesh. The Bradenton enclosure in Hillwood Preserve is fitted with upgraded Super Screen no-see-um mesh, and the Lake Jovita enclosure uses noseeum screening to reduce insects.

Where are no-see-ums a real problem around Tampa Bay?

Biting midges are best known in Florida as coastal pests. UF/IFAS Extension says several pest species use the marshes, swamps and mangroves of coastal Florida as larval habitat and can reach densities that drive people indoors. Other species develop at the edges of ponds and puddles.

Timing matters as much as place. Most species bite at dusk, at night or in the morning, but UF/IFAS Extension notes that in coastal areas many bite in broad daylight. Adults of many species fly about 2 km, so the marsh does not have to touch the property line.

UF/IFAS names beachgoers among the people these insects pester in coastal areas, which describes barrier-island communities such as Belleair Shore, where Pool Pros has built two Gulf-front pools. Seasonal nuisances are a separate question, covered in lovebug season and your pool.

What do you give up with no-see-um mesh?

A tighter weave means less open space, and open space is what you see and breathe through. Phifer’s glossary explains that higher-openness screens allow more light, improved air flow and better visibility, and that smaller-diameter yarns increase visibility and air flow. Phifer’s privacy page adds that a tighter, less open weave equals more privacy.

Phifer’s own descriptions of the 20x20 reflect both sides. The product page says no-see-um screen offers good ventilation and visibility, and the catalog adds that it provides some daytime privacy. Privacy and view are the same property seen from opposite sides of the screen.

Durability is not the trade. Phifer’s selection guide rates the 20x20 No-See-Um screen Best for durability and the 18x14 Better, and Phifer says both carry a PVC coating formulated for Florida’s UV exposure.

Does no-see-um screen add wind load to a pool cage?

The Florida Building Code treats the two meshes differently for wind. Table 2002.4 of the Building volume sets design wind pressures for screened enclosures, and its note 6 reads, in part:

Table pressures apply to 20 × 20 × 0.013“ mesh screen. For 18 ×14 × 0.013“ mesh screen, pressures on screen surfaces may be multiplied by 0.88. For screen densities greater than 20 × 20 × 0.013“, use pressures for enclosed buildings.

In plain terms, the code’s baseline mesh has the same 20x20 count as no-see-um screen. Under Table 2002.4, an engineer may design 18x14 screen surfaces for 0.88 of the table pressures, and screen denser than 20 x 20 x 0.013 inch takes the pressures for an enclosed building. The full-scale wind test report prepared for the Florida Building Commission used 18x14 fiberglass mesh on both enclosures it tested.

The practical consequence arrives at a rescreen. A cage engineered with the 18x14 reduction was designed for less pressure on its screen surfaces than the table sets for 20x20 mesh, so switching mesh is a question for the enclosure’s engineering, not only for the rescreening crew. The Pool Pros guide to rescreening a pool cage after a storm covers checking the frame, and the article on pool cage wind ratings explains where the engineering comes from.

How do 18x14 and 20x20 pool screens compare?

Feature	18x14 pool and patio screen	20x20 no-see-um screen
Yarns per inch (Phifer)	18 by 14	20 by 20
Designed for (Phifer)	Extra strength to span large openings	Keeping out the smallest flying insects
Insect protection rating (Phifer guide)	Good	Best
Durability rating (Phifer guide)	Better	Best
Insects named	Most insects (Phifer)	No-see-ums, gnats and sand flies (Phifer); biting midges excluded (UF/IFAS)
Wind pressure on screen surfaces (FBC Table 2002.4)	Table pressure × 0.88 permitted	Table pressure as printed

Which screen should you choose?

The right pool screen depends on the lot more than on the product:

• Coastal lot near marsh or mangroves: 20x20 no-see-um mesh, the screen UF/IFAS Extension says has openings small enough to exclude biting midges.
• Breezy inland lot where the view matters most: 18x14 pool and patio screen, which Phifer rates Good for air flow and viewing clarity.
• New enclosure: choose the mesh before the engineering is drawn, so the design matches the screen.
• Existing cage: ask what mesh the engineering assumed before changing it at a rescreen.

Both priorities show up on Pool Pros projects. The screen enclosures on Pool Pros builds page describes no-see-um mesh in Bradenton and Lake Jovita and a panoramic enclosure in Carrollwood built to keep sightlines open.