The most important factor in choosing a sock liner is the thickness of the insole. If you have minimalist or tight-fitting shoes, you’ll want a very thin sock liner to ensure that your feet have sufficient room in your shoes. Similarly, if you have roomy shoes or are looking to take up more volume in your shoes, a thicker sock liner is more appropriate. For a one-to-one replacement, try to find a replacement insole roughly the same thickness as the factory insole you’re replacing.