I came across this article which suggests horizontal stripes can make you appear thinner. It had previously been thought that vertical stripes gave a slimmer effect but an experiment has now disproved this theory. The University of York Psychology Department asked a group of people to decide which women looked slimmer in 200 pairs of pictures, some of which had horizontal stripes and some vertical. The result was that even though the women were the same size the horizontal stripes made the model appear thinner and further research found that the ones wearing the horizontal stripes were 6% wider. I'm off to buy some stripy clothes.