An octagon is a standard shape for a radar reflector, which are frequently attached to balloons to make them more visible to aircraft: https://www.thedrive.com

An octagon is a standard shape for a radar reflector, which are frequently attached to balloons to make them more visible to aircraft: https://www.thedrive.com/the-war-zone/china-seen-using-radar-reflector-balloons-to-defend-key-targets https://www.thedrive.com/the-war-zone/china-seen-using-radar... https://www.overlookhorizon.com/how-to-launch-weather-balloons/radar-reflectors/ https://www.overlookhorizon.com/how-to-launch-weather-balloo...