In terms of protein content, which is what causes gluten develop to develop in doughs, pastry flour is between cake flour and all-purpose flour with a protein content of 9.2 % protein.
Some prefer it not only for pastry, but also for “quick breads” such as soda biscuits, muffins and pancakes.
Substitutes
All-purpose or plain flour. To approach pastry flour more precisely, two parts all-purpose or plain flour to one-part cake flour.