Launch in calm weather conditions - foil balloons are tougher then latex however to acheive float they have very little free lift and so are very sensitive to damage, high winds, clouds and rain. It has been seen that sometimes the balloons aren't able to pass through a cloud layer. Another issue is that with a low ascent rate if there are high ground winds the balloon can travel quite far before getting above tree/pylon/building height and so is at an increased risk of getting caught. Rain can add mass to the balloon and payload which could result descent of the balloon. Suggested weather conditions: