Press Release: Natural Merino Wool Trumps Synthetic Polar Fleece for Baby Sleep, say Scientists

~ Baby sleeping bags are recommended by health professionals and used by an increasing number of maternity hospitals, but some sleeping bags are better than others ~

PORTSMOUTH, N.H. — Merino Kids today announced that scientists have found that babies sleeping in natural merino wool sleeping bags are less likely to overheat and less likely to become damp or chilled compared with babies sleeping in synthetic ‘polar fleece’ baby sleeping bags. The scientists at New Zealand’s largest Crown Research Institute, AgResearch, compared the Merino Kids merino wool baby sleep bag with the most widely-used polar fleece baby sleep bag and determined that the Merino Kids sleep bag had 80 times higher moisture vapor absorption to help keep a baby dry and comfortable throughout the night.

sleeping bags keep babies covered and warm and take the place of blankets which can cover a baby’s head. Head covering is identified as a risk factor of SIDS. Overheating an infant may also increase their risk of SIDS and the AgResearch team analyzed baby sleep bag properties that influence the thermophysiological comfort of sleeping infants. In other words, how the sleeping bags would affect the ability of a baby’s body to manage heat and moisture to maintain its normal thermal balance.

The results of the scientific study indicate that the Merino Kids merino sleep bag is likely the best option for maintaining a baby’s thermophysiological comfort and well being in a wide range of conditions. In particular:

  • The merino sleep bag was found to have moisture vapor absorption over 80 times higher than the polar fleece sleep bag. This means that a baby sleeping in the merino sleep bag would be less likely to get damp in areas where moisture vapor transmission is restricted, such as between baby and mattress. Babies often get damp while sleeping, from, for example, condensation of perspiration.
  • The merino sleep bag was found to have lower air permeability but the same moisture vapor transmission as the polar fleece sleep bag. The lower air permeability means that in a merino sleep bag the baby is better protected from chilling from normal air movement such as drafts or air conditioning.
  • The Merino Kids sleep bag was found to have lower thermal resistance than the polar fleece equivalent as a result of its different knitted fabric structure rather than the different constituent fiber. This lower thermal resistance means that the baby is less likely to overheat in the merino sleep bag. The high thermal resistance of the polar fleece sleep bag, which means it is warmer in completely still air, would be of value in cold environments without airflow. Any normal airflow in the baby nursery would reduce this thermal resistance because of the polar fleece sleep bag’s lower air resistance. If the room temperature rises, the polar fleece sleep slack might result in the baby becoming uncomfortably hot and damp because of polar fleece’s low moisture vapor absorption.

Dr. Stewart Collie, Senior Scientist at AgResearch, concluded: “Our thermophysiological comfort test results, combined with wool’s natural low flammability, its volatile gas absorption properties and non-irritant properties, all indicate that merino wool is the ideal fiber type to use in infant sleeping bags.”

Merino wool is a natural renewable resource, re-growing on the merino sheep after shearing. Polar fleece, also known as ‘microfleece’, is a synthetic material derived from non-renewable petrochemical sources invented to mimic wool.

Evolution has endowed the merino sheep with an amazing fine wool fiber with beneficial properties yet to be replicated by synthetic fabrics. Merino clothing is worn by top athletes and adventure sports enthusiasts due to its remarkable natural ability to regulate body temperature; it readily absorbs and releases moisture to keep the wearer warmer in cold conditions and cooler in hot conditions.

“We have always known that merino is best for baby and here is scientific evidence proving it,” said Amie Nilsson, founder of Merino Kids. “Merino is nature’s smart fiber whereas polar fleece is plastic in disguise. I hear often from parents that with polar fleece sleeping bags their babies wake hot and clammy, and some developed a heat rash. This is not the case with natural merino. Our award-winning merino sleeping bags keep babies and toddlers warm, dry and sleeping through the night.”

Click here to read the report Product Comparison of Merino Wool and Polyester Baby sleeping bags.

About Merino Kids

Merino Kids was founded in New Zealand in 2003 by Amie Nilsson who created the world’s first merino baby sleep bag. Today Merino Kids is the global industry leader in using natural merino wool for safer baby sleep.


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