This hat was based on Debbie New’s garter stitch Klein bottle hat. (Debbie’s pattern is not currently available.) It is a very interesting construction and totally different from her Ribbed Klein Bottle Hat

It was made for a talk, entitled Wears the Maths, which I gave at Mathsjam 2012.

The model in the photos is David Singmaster who is a puzzle expert and will be well-known to puzzle fans. He told me he had always wanted a Klein bottle hat - so the hat went home with him.

(At the same event in 2011 David sowed the seeds for several possible projects which I have been working on ever since but none of them has come to fruition - yet!)

The hat was made from an unknown double knitting yarn, with no labels, which had been hanging around for many years. I’m glad it finally found a use.