One of the most common question from those interested to wear their babies seems to be "What is the maximum weight that this sling can hold?" or "How long can babywearing last... namely, until when can I wear my baby?"
The standard answer to those questions, from me, or anyone else selling the pouch type sling is that it can be used to carry a child up to 15 kgs.
Given suitable fabric, the sling can be much more durable and can even hold an adult! Think of hammocks... think of swings made of fabric... In fact, through my research, I have read about people carrying children that is 18 kgs.
The point is, it does not entirely depend on the fabric. Mainly, it depends on the endurance level and this vary greatly from one to another.
I have always been known as one of those girls who can be tough. I can lift boxes heavier than most girls can etc. In babywearing, with the pouch (i.e. one shoulder carry), honestly, I am only beginning to feel the strain when Arthur was approaching 12kgs. Prior to that, I can wear him for 4 hours straight when we were out shopping... he sleeping soundly in the sling. This has been what I have been telling people... "no strain til he was almost 12 kgs".
Recently, as I get together with more babywearing Mommas, I realised that not many have the endurance level as I. Some start complaining about straining their shoulders even when their little ones is only 9 kgs.
It really is an individual thing. Just as how some babywearers would not use the sling for cradle carry at all.
To top it, age is not a good indication either as for an example, my 3 1/2 year old niece is lighter than my little Arthur. So, there you go. My Sis still wears my niece when they are in crowded areas. Sis is a fan of Pasar Malam... and Sales... and Fairs... and Warehouse Sales... these are the occassions when she would use the sling... just to keep her close. Good idea, I think. And, even though it could be a bit tiring, she's admitting it's much better than having to carry her with bare arms, which doesn't leave her hands free enough to be checking things out ;)
Endurance levels is naturally increased as your baby grows, that is, if you have started wearing your baby since he/she is a newborn. Otherwise, if you are starting out with a toddler, a good thing to do would be to slowly build your endurance levels by slowly increasing the duration you wear your baby. Perhaps, 20 minutes for the first time... 30 minutes for the second time... etc. etc.