How mesh size is counted
Screen netting is named by the number of openings per inch. A 20 × 20 net has 20 openings per inch in both directions, so it is often called a 20 mesh net. The higher the number, the smaller the openings.
The real opening is 25.4 ÷ mesh count − strand diameter, in millimeters. A 20 mesh net with 0.25 mm strands has openings of about 1.27 − 0.25 = 1.02 mm. A 32 mesh net with 0.20 mm strands has openings of about 0.79 − 0.20 = 0.59 mm.
20 mesh vs 32 mesh
| Compare | 20 × 20 mesh | 32 × 32 mesh |
|---|---|---|
| Approx. opening | ≈ 1.0 mm | ≈ 0.6 mm |
| Keeps out | Moths that lay caterpillar eggs, flies, beetles and mid-sized insects | The same insects as 20 mesh, plus smaller ones such as leafminers |
| Ventilation | Better airflow | Less airflow, so it needs more screen area |
| Good for | Vegetable plots where caterpillars and larger insects are the main problem and good airflow matters | Greenhouses that need finer protection |
Opening sizes assume 0.20–0.25 mm strands and are approximate. Real insect sizes vary by species and life stage, so treat the table as a starting point.
Smaller insects
Some insects get through a 0.6 mm opening. Aphids and whitefly need openings of about 0.4 mm or less, and thrips need less than 0.15 mm. If these are your main pests, talk to our sales team before you order.
Finer nets, less airflow
A 32 mesh net lets less air through than a 20 mesh net, so a screened greenhouse can run hotter and more humid. These steps help:
- Add screen area: raise the side walls or build a frame that sticks out over the vents, so more air passes through the net.
- Use only the mesh you need: if your main pests are caterpillars and larger insects, 20 mesh is enough and ventilates better.
- Keep the net clean: dust and residue block the openings and cut airflow further.
Install it so nothing slips through
- Bury the bottom edge or weigh it down along its whole length, so there are no gaps at the base of the walls.
- Fit a double door and close the outer door before opening the inner one, so fewer insects follow people in.
- Check seams and tears regularly and repair them straight away: a small gap is enough for insects to get in.
Ordering
Our main screen netting sizes are 20 × 20 and 32 × 32 mesh, 60–500 cm wide, in 5–500 m rolls. Blue is normally kept in stock. For other mesh sizes, please ask our sales team.
