Short answer: significantly.
Long answer: The durability of shuttlecocks depends on many different factors such as the natural ambient humidity in your location, time of year, quality of shuttlecocks you use, air humidity and temperature in the badminton hall etc. However, by always storing your shuttles optimally - in a humid environment - you will essentially maximise the durability of the shuttles regardless of the ambient conditions.
Our tests have shown an improvement of up to 100% in durability, in other words, the shuttles have doubled in durability. On average, expect to see durability increase of anywhere between 40% to 60%.