The Essential Sleep SackThe Essential Sleep Sack made of natural cotton and linen blend. Lined with soft and natural 100% merino wool jersey and designed to create a microclimate around your baby that helps maintain a consistent temperature for peaceful sleeping. Breathable, hypoallergenic fabric is suitable for year round use and ideal for most indoor temperatures (68 74F). If you are looking for quality, this is the one! Great for passing down to sibling, cousin or friend.