So, what's the main difference between a good elastomer and a bad one?
The stress-strain curve.
As you can see on the left one, natural latex (and natural rubbers, based on it) have a final interval where pressure increases quickly. It allowes to inflate toys like this one:
>>2262 when one chamber is fully inflated, it resists further inflation and keeps enough additional pressure to inflate another one.
So, if you want an inflatable doll (like a balloon, not like a pooltoy), you need elastomer with left curve.
Another curve shows the worst thing an elastomer can have: necking. It means, it loses it's ability to hold the pressure as it gets thinner, so the envelope quickly develop a local bubble-like bloat and pop there like a bubble gum.
PVC, most silicones (and surprisingly metal foil) have wrong curve type, so PVC dolls are bad for over-inflating (stretching), and silicone must be enforced with an elastic fabric. It restricts stretching, providing that quickly rising slope on the left curve.
When you select an elastomer for your DIY doll (for example, uncured rubber sheets), read it's .PDF file for the stress-strain curve.