Ok. I've found the ideal target material.....from Lidls. Lidls have their chilled meats delivered in a thin white corregated cardboard boxes. They then unpack the boxes and chuck them away. Umarexs at 10 metres leave nice clean holes. I found my local Lidls was pleased to give me as much of this stuff as I could carry. You could probably silk screen the target straight onto it. The boxes are quite big and provide several A3 sized bits of card.
The ideal seems to be stiff but easy to penetrate. Sounds like a girl I used to know...