Fleece is an excellent fabric choice when selecting onesie pajamas; however not just any fleece will make great sleepwear. Big Feet Pajama fleece footed pajamas are made using premium100% polyester micro polar fleece. Micro polar fleece provides the soft warm comfy cozy qualities of polar fleece with less weight and better moisture wicking properties making it perfect for sleepwear. Our fleece is a premium micro polar anti-pill fleece. Anti-pill fleece is a higher quality more expensive fleece that is more durable and resists pilling. Anti-pill fleece will not ball up (pill) or pull apart like non-anti-pill fleece will during wear or most noticeably during or after wash and dry cycles. Please see images for size chart.