Most "full synthetics" are what had been referred to as "Synthetic Blends".
But to answer your question, the lower tier of 0W20 are blends of synthetic and refined mineral oils,
The upper tier products - Mobil 1 AP, Amsoil SS - are majority synthetic base oils from what we can glean from SDS and performance data like MRV and ASTM D5800.08 NOACK volatility.
And synthetic oil products are NOT made in a lab despite ridiculously incredible
Developed? Yes; Manufactured ? NO.