Special care must be taken because they do carry the most precious cargo. Be sure to check over your work and to regularly inspect it for wear. Use quality fabrics. Fabrics such as quilters cotton, flannel, and muslin are generally not suitable for baby carriers. An exception is osnaburg muslin which can be used. Other muslin such as baby muslin are better suited for trying out patterns. Good quality thread is also important. Store brand thread, such as Walmart thread, does not hold up as well.
Also, there are new regulations for the production of baby carriers. If you plan on producing baby carriers for sale you must be compliant with the CSPS regulations. There is no small batch manufacturer exception, if you sell any then you are subject to them. The Baby Carrier Industry Alliance is a great resource in navigating them.
Woven wraps only have stretch on the bias (diagonal). Popular fabrics to use for a DIY woven are osnaburg and 100% linen. Other fabrics can be used, however try to stay with natural fibers. Synthetic fibers such as polyester do not breathe as well and can cause overheating issues. When you select your fabric it should not have a really dense weave. If you hold it up to the light, some light will pass through. It should not be so flimsy that you can see right through it or poke a hole in it with your thumb. Lower quality fabric such as muslin (other than osnaburg which makes great wraps) and quilters cotton (all those pretty prints) are not recommended. Try to look in the apparel fabric. Another test you can do is to take the fabric, tightly wrap it around your hand, and pull to try to see if the fabric digs into your skin.
Once you select your wrap, then it is very important to pre-wash it. Many fabric can shrink considerably in the wash. After it is dry, then you should iron it. You might want to put on a long movie to watch while you do this bit. There are a couple different ways to try to cut the wrap to the desired width. I prefer to carefully fold the wrap in half until it is a couple feet long. Then I mark the width and use a straight edge and a rotary cutter to make the cut. After this then you can cut the desired length and add tapers if you wish. Tapers make the wrap shaped like a parallelogram They can measure anywhere from 10 inches to even 24 inches. And then finally, woven wraps should be hemmed. If you plan on later dying the wrap then you should use a cotton thread to hem as a synthetic thread will not take up the dye.
Another popular source of fabric is tablecloths. 100% cotton table cloths can make excellent short wraps. A 120x60 inch tablecloth can be split in half into two long size 2 wovens. The wrap pictured is Mahogany peacock tablecloth in teal/grey.
Proper ring choice is important for making ring slings. Craft rings which are the thin and shiny rings that can be found at many craft stores are not strong enough for wearing a child. You can also find welded rings at some hardware stores. While these may be strong, the welds can rub against the fabric of the sling and weaken it. This can also cause a safety issue. Rings made for the purpose of making baby carriers can be found at slingrings.com. These have been tested for safety and come in nylon and aluminum rings. Once again, stay away from quilters cotton and muslin unless for decorative elements. Gauze can also become unstable when sewn and should be avoided in single layers. Use caution with multiple layers. Use good quality thread, stay away from cheap thread like the Walmart brand. Look for Gutterman or other high quality threads.
Jan is the woman behind Sleeping Baby Productions, a local company out of the New Hampshire. She has graciously not only made her patterns available online, but even posted video of how she makes her slings. These are for personal use only. The patterns and items made from these patterns are not licensed for retail. Please respect her generosity and intellectual property.
Single Layer Sling: http://crafts.sleepingbaby.net/sling.html
Different Shoulder Styles: http://crafts.sleepingbaby.net/shoulders.html
There are many different instructions online on how to make your own. Here is a general overview for a reversible mei tai. The body can be as simple as a rectangle that is 16x18 inches for an infant or 18x20 inches for an older baby. Mei tai measurements do not include the waist, so be sure to add extra length for it. Personally, I use two layers of fleece for light padding in my straps and 4 layers for stiffer padding for my waist. Shoulder straps can be anywhere from 75-80 inches. You can leave them long and then mark where you want to hem them after trying it out. Wrap style straps are generally a half of the width of the wrap, so about 15 inches. You don't need to chop a woven to do a wrap conversion style mei tai. You can do wide straps other fabric or even do a faux wrap conversion with a DIY woven or tablecloth.