Here is a current UK issue mosquito headnet, as issued to troops on jungle operations or exercises.

Designed to be simply pulled over the head and secured round the neck with an adjustable elasticated cord with a cord-lock.

Ample room to be worn over a wide-brimmed bush hat if required...

These are brand new condition, complete with issue label etc.

'HEADNET, INSECT PROTECTION, ONE SIZE - NSN 8415-99-519-8268'

Laid flat measures 45cm top to bottom, and 45cm across at the neck, and 16cm diameter at the top.