Sometimes a simple tool works better than your hands alone, and that is true of this tip for rolling thin strands of polymer clay. The trick for rolling thin strands is to have well conditioned clay which is blended with a translucent clay to make it as elastic as possible.
Once you have the correct clay for this technique, use a rolling block to apply even pressure to work the clay thinner and thinner as you roll it. Although I often use the flat black of a polymer clay blade in a pinch, my favorite tool for thin strands is a clear acrylic block. Mine does double duty as a backing for clear stamps.
Start your polymer clay roll by hand, as shown in the photo. Spread your hand across the block to apply pressure evenly across the width of your polymer clay, and roll it forward and backward on a clean flat working surface. I use a piece of tile or a section of tempered glass.
As your roll of clay extends beyond your rolling block, cut the roll in half, and continue to stretch and roll it as thin as possible using the block. If you see the roll of clay bunching or stretching in odd directions (why the clear block is a great tool!) stop and clean your work surface, or recondition the clay. Sometimes clay which is not fully mixed will 'shred' as you work it.
This works for air dry and polymer clays, and gives you a smaller clay strand than you can usually make by hand. It is an easier method of making fine strands than using a polymer clay extruder, especially if you prefer to work with firm clays. See the second photo in the set linked to this page to see how much finer a line you can roll with a flat surface, as opposed to extruding through the fine plate of a clay gun.