Orthotic sandals for arch support and plantar fasciitis

What material are these made from? Is it leather?

Has anyone used these whilst working standing up? I have a stand-up desk, on a wooden floor...would these be enough or would I also need a mat?

Would these be suitable for the swimming pool instead of the usual no-support flip flops? I go at least 3 times a week. Would getting wet spoil them?

I am uk size 5 which size should i order?