Pure Mulberry Silk Duvet Insert – Double Cocoon Fill, All-Season | HeartcosyNot all silk duvets are the same. This one starts with the fill. Most silk duvets use short strand or mixed silk that compresses over time. This duvet is filled with 100% double cocoon mulberry silk a construction that uses the entire continuous filament from two interlocked cocoons, hand stretched into layers for even loft and long lasting resilience. The difference you feel on night one, you'll still feel three years later. The fill: Double Cocoon