After my much loved self inflating pillow sprung a leak (seam around the valve) I pretty much gave up on it and resigned it to the 'collection of broken things'. It was never that light at 185g and didn't pack very small. Being someone who likes to fiddle with things I decided to cut it open for a look. I couldn't believe how much foam was inside, no great wonder it weighs what it does.
Insides of a self inflating pillow + 'outer skin'
I turned it inside out and located the leak, which was handy considering it now had a great big cut down one side

I repaired the leak regardless and threw the foam in the bin ... all I had to do now was repair said big cut down one side. I was eventually allowed access to the iron and five minutes later I had a fully fuctioning air pillow.
New seam made with household iron.
It now packs down to about an eighth of it's former size and weighs 45g

... oh and it doesn't leak anymore.