Quick Answer
When choosing between Mylar and wool for warmth, consider the specific conditions you'll be in, the weight and packability you need, and the maintenance requirements of each option. Mylar provides excellent warmth-to-weight ratio and is lightweight, but it loses insulation when wet. Wool, on the other hand, retains some insulating properties even when wet, but it's heavier and bulkier.
Mylar’s Advantages and Limitations
Mylar, also known as space blanket or emergency bivvy, is an excellent option for extreme cold, wet, or windy conditions. Its reflective surface can retain up to 90% of body heat, making it ideal for survival situations. However, Mylar’s effectiveness drops to around 50% when exposed to water or high humidity. When choosing a Mylar bivy, look for a design with a waterproof and breathable membrane, such as a Gore-Tex or Sil-nylon shell, to minimize moisture accumulation.
Wool’s Benefits and Considerations
Wool is a natural insulator that retains some warmth even when wet. Merino wool, in particular, is a popular choice for outdoor gear due to its lightweight, breathable, and moisture-wicking properties. However, wool can be heavy and bulky, making it less suitable for lightweight backpacking trips. When considering a wool bivy, choose a design with a water-resistant treatment, such as a DWR (durable water repellent) finish, to extend its lifespan and performance.
Practical Considerations
When deciding between Mylar and wool, weigh the specific demands of your trip. If you’re planning a high-altitude, high-wind, or wet-weather expedition, Mylar’s reflective surface may provide the best warmth-to-weight ratio. In contrast, if you’re embarking on a shorter, warmer trip, wool’s natural insulating properties and breathability may be more suitable. Consider your personal preferences for pack weight, maintenance, and durability when making your decision.
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