I used the 210D fabric from the DIY Packraft shop for the multi-colour packraft how-to videos – you can see that it bonds quickly without melting. (I use the same temperature to bond the 40D fabric, too.)
I did a lot of research before deciding what fabrics to purchase for the DIY Packraft shop… I tested TPU-coated fabrics from other suppliers and many of them are not good for heat sealing because the melting temperature of the fabric is too close to the bonding temperature of the TPU, so the nylon melts before the TPU is bonded. It sounds like that is the problem many people are having with fabrics sourced elsewhere.
In general, you should only use nylon-66 because it is stronger and has a much higher melting temperature.