My 9 year old son Aidan loves maths. I think he probably gets it from my dad, but he certainly doesn’t get it directly from me!

He’s been wanting me to make him a Klein bottle hat since he saw Matt Parker on television giving a talk about 4D and stuff at the Royal Institution.

A Klein bottle, according to Aidan, is a 3D shadow of a 4D mobius loop. A mobius loop is when you take a strip of paper, twist it then stick the ends together. Mathematicians get very excited about them. A Klein bottle is a tube version. In 3 dimensions it will intersect itself but in 4 dimensions it can wrap around itself without intersecting.

Just typing that has fried my brain!

Anyway, Matt Parker has a Klein bottle hat that his mum knitted him, but this was before I discovered that I was a knitter and I needed a crochet pattern.

I like a challenge, so Aidan drew me a picture and with a little bit of googling I came up with a design for a Klein bottle hat.

Aidan chose the yarn himself. It’s King Cole Riot Chunky in colour 1953 cosmic. The colours are beautiful. If you saw the picture on Instagram, I didn’t even use a filter. The colours were so bright it didn’t need one! It’s lovely and soft, perfect for a child’s hat, and being chunky it grew nice and quickly!

The hat is basically 2 hats joined at the top by a tube, with a slit in one of them to allow the tube to pass through. I can’t crochet in 4 dimensions!

How to Crochet a Klein Bottle Hat

I used most of 2 100g balls of yarn, and a 6 mm crochet hook. The hat fits the head of a 9 year old. It’s probably best to check against the head that you’re making the hat for and adjust if necessary.

When you finish each round, join it with a slip stitch, then turn around and go back the way you came. This is so that it doesn’t look odd when you make the slit in the outer hat.

Make 70 ch

Round 1 2 ch, 1 tr into 3rd ch from hook, *1 tr into each st to end of round.* Join with ss.

Rounds 2-6 2 ch (counts as 1st stitch), 1 tr into 2nd st from previous round, *1 tr into next st* to end of round. Join with ss.

Rounds 7-8 2 ch (counts as 1st stitch), 1 tr into 2nd st from previous round, 1 tr into next 3 st. Crochet together the next 2 st. *1 tr into each next 5 st, then crochet the next 2 st together* to the end of the round. Join with ss.

Round 9 2 ch (counts as 1st stitch), 1 tr into 2nd st from previous round, *1 tr into next st* to end of round. Join with ss.

Round 10 2 ch (counts as 1st stitch), 1 tr into 2nd st from previous round, 1 tr into next 3 st. Crochet together the next 2 st. *1 tr into each next 5 st, then crochet the next 2 st together* to the end of the round. Join with ss.

Round 11 2 ch (counts as 1st stitch), 1 tr into 2nd st from previous round, *1 tr into next st* to end of round. Join with ss.

Rounds 12-14 2 ch (counts as 1st stitch), 1 tr into 2nd st from previous round, 1 tr into next 3 st. Crochet together the next 2 st. *1 tr into each next 5 st, then crochet the next 2 st together* to the end of the round. Join with ss.

Rounds 15-16 2 ch (counts as 1st stitch), 1 tr into 2nd st from previous round, 1 tr into next st. Crochet together the next 2 st. *1 tr into each next 3 st, then crochet the next 2 st together* to the end of the round. Join with ss.

Rounds 17-31 2 ch (counts as 1st stitch), 1 tr into 2nd st from previous round, *1 tr into next st* to end of round. Join with ss.

Rounds 32-33 2 ch (counts as 1st stitch) 1 tr into 2nd st from previous round, 1 tr into next 2 st, 2 tr into next st, *1 tr into each next 4 st, 2 tr into next st* to end of round.

Rounds 34-36 2 ch (counts as 1st stitch) 1 tr into 2nd st from previous round, 1 tr into next 4 st, 2 tr into next st, *1 tr into each next 6 st, 2 tr into next st* to end of round. Don’t join these rounds!

Round 37 2 ch (counts as 1st stitch), 1 tr into 2nd st from previous round, *1 tr into next st* to end of round. Don’t join this round.

Round 38 2 ch (counts as 1st stitch) 1 tr into 2nd st from previous round, 1 tr into next 4 st, 2 tr into next st, *1 tr into each next 6 st, 2 tr into next st* to end of round. Don’t join.

Round 39 2 ch (counts as 1st stitch), 1 tr into 2nd st from previous round, *1 tr into next st* to end of round. Don’t join.

Rounds 40-41 2 ch (counts as 1st stitch) 1 tr into 2nd st from previous round, 1 tr into next 4 st, 2 tr into next st, *1 tr into each next 6 st, 2 tr into next st* to end of round. Join with ss.

Rounds 42-48 2 ch (counts as 1st stitch), 1 tr into 2nd st from previous round, *1 tr into next st* to end of round. Join with ss.

Push the first hat through the slit you made in the second hat. 

Line up the bottom edges of the hats. Check that the lines where the rounds are joined are together. Dc the 2 hats together.

Aidan is very happy with his hat, so much so that he even agreed to model the hat so that I could take some pictures. Usually he hates having his photo taken!

Tips

If you are making the Klein bottle hat for a larger or smaller head, just adjust the number of stitches you start with, then follow the pattern.

The 2 hats need to be roughly the same size. If, when you get to Round 42, you find that you have a different number of stitches to what you started with, use the next couple of rounds to make adjustments by increasing or decreasing until you end up with the correct number of stitches.

If the 2nd hat seems a little short, then add an extra row.

Feel free to add a picot edging if you are making the hat for somebody who might like it!