Phil links to some excellent products:
➥ Mosquito Netting vs. No see um netting comparison
Mosquito net mesh size should be large enough for air circulation, but as small as possible to keep out the mosquitoes.
A mesh size of 1.2 mm x 1.2 mm is the most common and recommended.
For effective malaria protection, the mesh size that is recommended is 120-200 holes per square per inch.
The small sand fly, however, which also transmits diseases to humans, can pass through this mesh size, and can only be avoided with a small-meshed mosquito net (0.6mm x 0.6 mm).
Use a denier (strength of fibre used to make net) that is between 70 and 100. The strongest is 100; anything below 70 usually tears easily.