I'm trying to built a silk version of the garment. Since my wool gambeson overheats. I already have dupicioni as the inner shell with silk velvet as the outer shell. Could Silk fiber recycled thread work as paddling? As I found 18oz of it for 30$.

3lbs equals to 48 oz. What does the document refer to the one worn under the armor or the stand alone version? I avoid cotton as it heats more than my old model. I'm fairly lean at 130lbs and 5'9" and expected less material, but considering the physique during the middle ages, it would be an accurate estimate.

It's the 1296 Ordonnances des Metiers de Paris, which requires armourers make neither coat nor gambeson with less than 3 livres of cotton (about 50 oz. or 1.48 kg) to be used for the fill along with rags or fabric scraps. Laws like this are usually enacted because someone tried to use less fill (since it's hidden from view) to save production costs while cheating the buyer.

While the regulation doesn't state whether this is a to be worn in conjunction with armor or by itself, we have accounts of knights wearing a gambeson, mail, and a sleeveless gambeson over the mail. Expect it to retain body heat, regardless of the type of filling material: cotton, tow, wool, silk, etc..