What is a notable drawback of using down insulation?

Down insulation is widely recognized for its excellent warmth-to-weight ratio and compressibility, making it a popular choice for outdoor gear like jackets and sleeping bags. However, one of its notable drawbacks is its performance when wet. When down insulation becomes wet, it loses a significant amount of its insulating properties because the feathers clump together, reducing their ability to trap air — which is essential for insulation. This means that while down is highly effective as long as it remains dry, exposure to moisture can seriously compromise its effectiveness, making it less reliable in wet conditions compared to synthetic alternatives.

The other options address different characteristics of down insulation but do not represent its primary drawback. For example, down insulation is often favored for being lightweight and highly compressible, and while it can be more expensive than some synthetic options, cost alone isn't the most significant concern when evaluating its practical use in varying environmental conditions.