Sorry for the confusion – I guess I need to make this clearer somewhere (or maybe several somewheres).
The lighter fabrics (e.g. tube fabrics, seam strips, inflation bag fabric) are coated with TPU on one side only, and the woven fabric is exposed on the other side.
The heaver fabrics that are used the in packraft floors are coated with TPU on both sides, so the orientation doesn’t really matter. The newer floor fabric presently used in the kits (the 450 GSM fabric) still has TPU on both sides, but one side has a glossy finish and the other has a matte finish, and I think that that difference in appearance is causing some people to assume only one side has a TPU coating.
When ironing the fabrics together, you can only press your iron against a surface that isn’t coated in TPU, so in any situation where you’re welding something to a piece of floor fabric, there’s only one way to do it (by pressing your iron on the woven fabric side of the other piece of fabric).
Does that make sense?