From Cocoknits --
"I wanted to supply a way for users to make sure their knits were blocking to their desired measurements, but there was no way to print accurately and safely onto the Knitter’s Blocks. So I designed a thin cotton cloth, woven to 1" / 2.5cm square gingham. The thread is pre-treated before the fabric is woven to prevent stretching, shrinking, or distortion. Lay it under your knitted item to get straight edges and measurements."