- Look at the tag that came with the liner. This has the care instructions and lists the material the liner is knitted from. However, if you were the lucky recipient of a hand-knit helmet liner, you might not know what kind of material it is. Is it knitted of acrylic or wool? It can be hard to tell. To be on the safe side, treat the liner like it's made out of wool, so you won't shrink it.
- To wash wool liners (or acrylic liners you think might be wool; this method won't hurt acrylic), hand wash it in cold water. Obviously, if you are using a military helmet liner and are out serving in the field, you won't be carrying around Woolite, so just substitute whatever liquid laundry soap you have. A gentler soap, if you have the choice, is best. Use a very small amount. Let the helmet liner dry flat, and avoid placing it in direct sunlight, if possible.