Basically, you make something like ring mail. Choose a durable fabric for this, such as denim. To make it permanent, add a layer of padding on each side, then cover that in nice fabric and quilt it all together.
To make a removable weighted liner, consider sewing the washers between two layers of cotton sweatshirt material, which is both tough and cushy, then put your duvet cover on the outside.
Note that a weighted blanket should be about 10% of your body weight. For some people this is too light, for others too heavy, so test before you sew. Get that amount of washers, put them in baggies, and pin them to a blanket for testing. Adjust the weight as desired.
Keep the thing on for as long as you'll be using it -- some people find that the weight starts making a body part ache after a few minutes or an hour, let alone overnight. If you make your own blanket, you can put the weight just where you want it, like leaving your feet unweighted.
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To make a removable weighted liner, consider sewing the washers between two layers of cotton sweatshirt material, which is both tough and cushy, then put your duvet cover on the outside.
Note that a weighted blanket should be about 10% of your body weight. For some people this is too light, for others too heavy, so test before you sew. Get that amount of washers, put them in baggies, and pin them to a blanket for testing. Adjust the weight as desired.
Keep the thing on for as long as you'll be using it -- some people find that the weight starts making a body part ache after a few minutes or an hour, let alone overnight. If you make your own blanket, you can put the weight just where you want it, like leaving your feet unweighted.