If you discover that a winter hat has a unique combination of materials like, for example, 70% acrylic, 20% polyester, and 10% wool, then there is no need to worry. I would personally recommend that you buy a hat that is 100% of a single material, just for the reason of avoiding potential headaches. There may be a material that you really can’t wear because of an allergic reaction to it, so in that case, don’t buy such a hat. Otherwise, feel free to buy hats with more than one material.