Ayiyoy 100% Pure Silk Night Sleep Cap Sleeping Beanie Hat Cap Made in 100% mulberry plain silk Size M Suitable for head circumference 20.87"-22.83",Size L Suitable for head circumference 22.05"-25.59" With cap sleep can keep your head temperature, reducing heat loss (75% body heat dissipation from the head), which can prevent colds Physiologists study confirmed that wearing socks to bed wearing a hat person, leg and head and neck vessels were diastolic state, blood smooth, can fall asleep quickly, many patients often intractable insomnia without medication IF YOU HAVE VERY LONG HAIR AND A LARGER HEAD -- this might be a bit small (please refer to the following description, describe the distinction between real silk and chemical fiber silk)