Homemade sleeping bag: sewing two blankets and the compression myth

Two sewn-together blankets are not a sleeping bag: the trick lies in the layers

Can you make a sleeping bag by sewing two narrow two-metre blankets together? The short answer is yes, as long as you understand what a sleeping bag really is and don't confuse it with wrapping yourself in fabric. The long answer involves three layers, a zipper, and a debate over whether the invention works indoors or is only good for keeping a low profile next to a dumpster.

The starting point is a household premise: two two-metre-long, narrow blankets joined at the edges make a fabric tube. So far, intuition works. The problem appears when you compare that tube with a commercial sleeping bag, which is not a single piece but a system of layers with different functions.

What layers a sleeping bag has and what each one is for

The structure discussed in the conversation is clear: a waterproof outer shell, a warming lining, and a cotton or similar inner layer. The outer shell is usually nylon or some plastic; the lining is that white fluffy fibre found in cheap cushions; the inside is cotton. With two blankets you can sort out the inner layer and the lining, but not the barrier against water.

That's where the emergency trick comes in: black bin bags or the tougher blue ones from big-box stores. The recommendation is to tape them to the blanket so as not to make holes where moisture can get in. In other words, the textile DIY works, but it turns the invention into a hybrid between blanket and plastic that loses breathability.

Why does a sleeping bag compress and a blanket doesn't?

The question left hanging is technical: if a sleeping bag is fabric, why does it compress and a blanket doesn't? The difference is not in the weave but in the filling and how it is arranged. A commercial sleeping bag uses fibres or down that compact and regain volume; a thick household blanket is not designed for that and takes up fixed space in the backpack.

Hence the practical warning: even a cheap summer sleeping bag is still more portable than two sewn-together blankets. The advice given is to look at the budget models from a big sporting goods chain before taking up the needle and thread. Compression, not warmth, is what you pay for.

Indoors, outdoors and the zipper detail

If you're sleeping under a roof, the outer waterproof layer is unnecessary. And if the waterproof layer is unnecessary, so is the sleeping bag shape: a folded blanket does the job. The implicit consensus is that the invention makes sense when there's moisture, not when there's a mattress and a wall.

The detail forgotten in the initial enthusiasm is the zipper. Without it, the fabric tube forces you to climb inside like into an envelope. With it, you can open and close it. And if instead of blankets you sew two sheets together, you get a summer bag, lighter but with no insulating capacity.

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In the end, the homemade sleeping bag exists, but it doesn't compete with the commercial one in weight or volume. It competes on price, and even then it loses if you count the sewing time. The sewn blanket keeps you warm; the sleeping bag, on top of that, is portable. That's the whole difference, and it's not a small one.