I purchased a piece of foam insulation that wraps around the coolant pipes on a home air conditioner. You can get it at hardware stores for about $2(US) in a 6 foot length.
Just cut a piece about 1-1/2 to 2 inches wide with a sharp knife or scissors. This is similar to what Cardiosport and some other manufacturers use. It will be just slightly smaller in diameter than the average(??) wrist.
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The Lord is merciful and gracious, slow to anger and abounding in steadfast love. - Psalm 103:8
I am a cyclist. I am not the fastest or the fittest. But I will get to where I'm going with a smile on my face.