Reply from the manager of Abakhan, Shrewsbury ...
Hi Imi, as this was a piece from our rems baskets there’s no way of knowing the exact content of the fabric, but I’d say it’s most likely a poly cotton. I’ve found another piece to gauge the weight and I’d imagine just a standard universal 70 needle would be fine for working on it. Depending on how many layers/other fabrics you’re sewing through you may need to perhaps go up a size, but I think you’ll be ok with the 70.
Top stitching done, perfect stitches (3.5 L) from the Splurgess (as expected) fabric sewed like a dream ... Pics of the dress later but here's a close up of the Top stitching ...