Lightweight silks are very slippery and shift offgrain easily. Take care when cutting since these fabrics will not hang properly if they are cut off-grain. It is easier to straighten fabrics on a surface with a grid such as cardboard or rotary cutting mat or a grain cloth. When fabric is particularly difficult to control, spread it on a flannel-backed vinyl cloth.
Source- Clair Shaeffer's Fabric Sewing Guide 2nd Edition