I have some screens that are the conventional fiberglass mesh that you would find in a screen door or on your windows at home. Great for MOST occasions. If you get to the areas where No-See-Ums are buzzing around they will fly right through that, and did for us last summer. I do think that air circulates better through the bigger mesh but there are a few bugs that might get through it as well.
2005 5.4L E250 RB50 4x4 SMB
2000 4Runner Limited 4WD
But God demonstrates his own love for us in this: While we were still sinners, Christ died for us. Romans 5:8