Recently I retired some of our cloth diaper covers, the last of the ones that we bought for our first baby. I had been extending them for the last baby, who had outgrown them, by pinning them on with the diapers, but the baby started escaping from them regularly.
To replace the diaper covers, I made several new ones: two layers of fabric with a layer of plastic enclosed in between. For a pattern, I traced around a secondhand pocket diaper that we use as a diaper cover. It has no elastic around the leg openings, yet it manages to achieve a decent level of containment.
For plastic, I used ironed-together chip bags for one, and stole my bulk
rice bag sewing machine cover for the other. The rice is both tougher
and more flexible.
The sewing procedure is very similar to making prefold cloth diapers, which for some reason I can't find any decent directions for, so: take the fabric for one side, sew the innards to it on the "wrong" side, then add the fabric for the other side with the "right sides" together and sew around the edges--but leave a gap so you can turn it right side out, and then once it is turned, sew the gap closed. For diapers, I also topstitch around the edges to keep them from inverting in the wash.
For closures, I experimented with using elastic ponytail holders and large (coat) buttons, sewing on the elastics where the tension would keep the loops secure on the buttons.
In practice, this works fairly well, although it would be better to have two elastics per side, so that the back edge doesn't pivot outward and make a gap around the leg. The buttons I used are large enough that no additional buttons are needed for this.
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Then I made a new cover for my sewing machine, using a nice fabric remnant that was handed down to me, that was too small for a pillow cover.
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I took some water bottles that were getting in the way, filled them with water and two drops of chlorine bleach each, and put them aside for use in emergencies and outings.
Buying chlorine bleach at the grocery store was annoying. New versions have been introduced since the last time I bought any, in the Pre-Covidian Era. Now there are fabric-preservatives and new scents added to most of them.
I also use bleach to turn black cotton clothing into brown cotton clothing, socks in particular. The key is to use very little bleach in sufficient water, and to rinse thoroughly right afterward.