I wanted a simple solution to prevent flies and mosquitoes from entering when I open the windows.

• I have some aluminium profiles used for LEDs like this ones 
• I have some leftover lill IKEA sheer net curtains 
• I have a window with rings (apparently they're called sash eyes)
• I have a 3d printer

So after making sure the profiles and the curtain have the correct length for the window, just roll a bit of net around the profile, install the connector, another profile at the bottom of the window to hold the net in place and voila, an insect net.

I printed with draft quality (0.24mm) at high speed without supports or brims using ABS (so that it can be a little flexible), and used a wall count of 4 (but I don't think it was necessary).

The onshape doc with parameters for different sizes and thickness can be found here