If you take one thing from this page, take this: protection comes from the aperture, durability comes from the yarn. A spec sheet that only says “150D” tells you nothing about what the net will stop. A spec sheet that only says “156 mesh” tells you nothing about how long it will last.
Mesh density is two numbers, not one
Almost every sourcing conversation about mosquito netting starts with a single figure, and that single figure is usually wrong. The industry routinely describes two completely different properties with overlapping language, and the overlap costs buyers real money.
The two properties are:
- Aperture (or mesh opening) — the physical gap an insect has to pass through. Measured in millimetres. This is the number that decides protection.
- Yarn specification — how thick the filament is, normally given in denier. This decides weight, bursting strength, light transmission, pack size and how quickly the fabric wears out.
They interact, but they are not interchangeable. Two nets can share a denier and behave completely differently, and two nets can share a mesh count and last for very different lengths of time. The rest of this page separates them, because every sourcing decision depends on keeping them apart.
What 156 holes per square inch measures
156 holes per square inch is an area count: the number of openings you would find in a one-inch square of fabric. In metric terms the same figure is written as 24 holes per cm². It is the figure most often quoted as the WHO-recommended minimum for mosquito netting, and it appears in procurement documents for insecticidal nets.
Two details matter here, and both are commonly mishandled:
It is an area count, not a linear count. A 156 HPI fabric has roughly 12.5 openings along each linear inch. When a supplier says “156 mesh” and a buyer hears “156 holes across one inch,” the two are off by a factor of about twelve. This confusion is the single most common error in mesh specification.
It was set for treated nets. The 156 figure became the reference point for long-lasting insecticidal nets, where the chemistry on the yarn does part of the work. For an untreated net — the kind used in camping tents, hammocks and travel nets — buyers usually specify the aperture directly in millimetres, because an aperture can be measured on the finished fabric and verified on delivery.
That is why serious spec sheets for outdoor netting lead with “1.2 mm opening” rather than “156 mesh.” Both numbers describe the same target, but only one of them is measurable with a ruler.
What denier measures
Denier is the mass in grams of 9,000 metres of the yarn. That is the entire definition. It is a linear density unit borrowed from the silk trade, and it describes the yarn, never the hole.
Useful reference points for polyester filament:
- A 30D filament is roughly 0.09 mm in diameter.
- A 75D filament is noticeably thicker, which makes the fabric heavier, more opaque and slower to dry.
- Household sleeping nets typically run 30–50D. Camping nets run 40–70D. Heavier industrial screening runs 70–100D and above.
Here is the consequence that buyers miss. Aperture depends on both yarn diameter and how many yarns are packed into an inch. Thicker yarn eats into the opening. If you increase denier and hold the mesh count constant, the openings get smaller — but the fabric also gets heavier and less breathable. If you increase denier and hold the aperture constant, the mesh count drops.
So “150D” and “300D” are not two points on a protection scale. They are two points on a weight scale. A 300D net is not twice as mosquito-proof as a 150D net. It is roughly twice as heavy per unit length of yarn, and it may well have larger holes if the weave was loosened to compensate.
The insect-to-aperture map
Protection is a matching exercise. You pick the aperture to the insect you actually have, then pick the yarn to the durability you need. Working from the wrong end — picking a denier and hoping — is how buyers end up with a net that looks dense and still lets midges through.
| Insect group | What it means in practice | Spec to put in the PO |
|---|---|---|
| Mosquitoes Anopheles, Aedes, Culex |
Body girth around 1.2–2.0 mm; they can flatten and push through gaps. This is the group the 156 HPI figure was built around. | 1.2 mm opening or smaller; 156 HPI minimum; 40–50 gsm |
| Sandflies Phlebotominae |
Smaller than mosquitoes. A 1.8 mm opening no longer gives reliable protection, which is why coarse tourist nets fail in sandfly country. | 1.0–1.2 mm opening, stated in mm not in mesh count |
| Biting midges Ceratopogonidae, “no-see-ums” |
Far smaller again. Standard mosquito mesh is effectively open to them; they pass through a 1.2 mm weave without difficulty. | 0.6 mm opening or finer; usually sold as 500+ HPI “midge-proof” grade |
| Black flies Simuliidae |
Stockier than midges. A 1.2 mm mesh blocks most of them; a midge-grade weave removes the doubt. | 1.2 mm for most uses; 0.6 mm for head nets in peak season |
Read that table as a warning about product claims rather than a buying guide. A tent described as a “mosquito net tent” is making a claim about mosquitoes. It is not making a claim about midges. In Scotland, in Nordic lake country, in Florida scrub and along much of the Canadian Shield, the insect that ruins the trip is not a mosquito. It is a midge, and the tent that was sold as protection does nothing.
Why 100 HPI fails the cone bioassay
The WHO cone bioassay is the reference test for insecticidal netting. A fixed number of susceptible mosquitoes are confined in a cone against a sample of the net for a set contact time, and knock-down and mortality are recorded afterwards. It is a functional test: it does not care what the label says, only what happens to the insects.
A 100 HPI net is coarse enough that Aedes aegypti can pass through the openings or avoid sustained contact with the treated surface. Mortality then falls below the acceptance threshold, and the net fails — even if the yarn is correctly specified and the insecticide dosage is correct. The failure is geometric, not chemical.
The operational lesson for buyers is blunt. If your supplier's “150D” net is actually a 100 HPI weave, it will not pass a tender's bioassay. The denier on the label will be accurate and irrelevant at the same time. Protection was lost in the reed, not in the yarn.
For untreated netting there is no bioassay to appeal to, so the aperture has to be verified directly. That is a measurement problem, and it has a cheap solution: count the openings under magnification on a one-inch span, and confirm against the millimetres declared on the spec sheet.
How to read a mesh spec sheet
A complete mesh line has five fields. Anything less and you are guessing at least one of them:
| Field | What a usable spec says | What a vague spec says |
|---|---|---|
| Aperture | “1.2 mm ±0.1 mm opening, measured on finished fabric” | “fine mesh” |
| Mesh count | “156 holes/inch² minimum (24/cm²)” | “high density” |
| Yarn | “100% polyester multifilament, 30–50D” | “150D” with no fibre named |
| Weight | “40–50 gsm, ISO 3801” | weight omitted |
| Air permeability | “≥800 L/m²/s” | weight and permeability both omitted |
If a supplier cannot give you the aperture in millimetres, that is not a detail to negotiate later. It is a signal about how the product was specified in the first place.
What this means when you buy
Three habits separate buyers who get what they ordered from buyers who get what was convenient to ship:
- Write the aperture, not the mesh name. “1.2 mm ±0.1 mm, measured on finished goods” is testable. “156 mesh” invites interpretation.
- Match the aperture to the insect you are selling against. Mosquito-grade for mosquito markets. Midge-grade if your customers are in midge country — and say so on the packaging, because a customer who buys mosquito-grade netting for a midge problem will conclude the product is defective.
- Ask for one test report per batch, not one per relationship. Denier (ISO 2060), weight (ISO 3801) and bursting strength (ISO 13938-2) are the three fields that catch most substitutions.
We work with audited weaving partners rather than operating a mill, which means our leverage comes from specifying precisely and inspecting before shipment. If you are comparing quotes, ask each supplier for the same five fields above and compare the numbers, not the adjectives. Send us your aperture target and we will tell you what is achievable at your volume.