What Size Mesh Stops All Insects?

The short answer is that no single mesh size guarantees 100% exclusion of every insect, because insects vary dramatically in size. However, if your goal is to block the smallest common pests—particularly biting midges (often called "no-see-ums" or sandflies)—you need a mesh count of at least 20x20 or finer.

Understanding Mesh Count

Mesh count refers to the number of openings per linear inch in both directions. For example:

• 17x14 mesh: 17 openings horizontally and 14 vertically per square inch
• 20x20 mesh: 20 openings in both directions, creating smaller apertures

The higher the mesh count, the smaller the holes—and the smaller the insects that can be excluded.

The Tightest Options

As your reference text notes, standard patio screens (typically 17x14 or 18x14) will block mosquitoes and most flying insects but will not stop no-see-ums. For complete protection against these tiny pests:

• 20x20 mesh is the minimum recommended density for excluding no-see-ums
• 20x30 mesh (such as solar insect screens) offers the tightest weave commonly available, providing maximum protection against even the smallest insects

Important Considerations

While finer mesh provides better insect exclusion, there are trade-offs:

• Airflow Reduction: Higher mesh counts restrict airflow. A 20x20 mesh can reduce airflow by 30-50% compared to standard 18x14 screening. This can make enclosed spaces stuffy, particularly in warm climates.
• Light Reduction: Tighter weaves also reduce visible light transmission. Solar screens (20x30) are designed to block heat and UV rays, which means darker interiors.
• Visibility: Very fine mesh can be more difficult to see through, potentially obstructing views.

Practical Recommendations

• For home windows and doors in areas without no-see-ums: Standard 18x14 or 18x16 fiberglass mesh is sufficient and provides good airflow.
• For patios, porches, or camping in no-see-um territory: Choose 20x20 mesh or specialized "no-see-um screening" available from outdoor and hardware suppliers.
• For maximum protection (tropical areas, near standing water): Consider 20x30 solar mesh, which blocks insects, reduces heat, and provides UV protection—but accept that airflow will be significantly reduced.

The Bottom Line

If you need to stop all insects, including the tiniest biting midges, select mesh with a count of 20x20 or higher. For absolute maximum protection, seek out 20x30 mesh. Remember that proper installation—sealing all edges and ensuring no gaps—is equally important as mesh size. Even the finest mesh is useless if insects can find an unsealed entry point.