Primaloft question

Confused by photos on sites that sell it, is this loose fill (down) or batt?

Batt. This site explains it well (and is interesting as it includes the history): https://backpackers.com/outdoor-guides/backpackers-guide-to-synthetic-insulated-jackets/

Okay, so since it is a batt it doesn't have to be stuffed into baffles, but can be sewn in as a single piece. Thanks.

Not stuffed, no, but not sure about sewing in a single piece, if I understand you correctly (and I probably don't). I think you still need to 'tack' it in various places to ensure it doesn't slip down to the bottom, as it were.

My thinking is to sew it to the material around all 4 edges, but leave the center mass unsown. This would work only if the insulation is in a batt, not loose fill.

This works with Climashield, but not necessarily for Primaloft. If you recall, the article says that Climashield uses long staple fibers where Primaloft uses short staple fibers to achieve a loft and feel similar to down. What this means is that, even though Primaloft starts as a batt, the fibers could shift and clump if they are not periodically tacked. I've used Climashield, but not Primaloft, so I can't comment from experience. I've seen where people have made Primaloft quilts with loose tacks every six inches or so. You can try it without the tacks, but if the insulation moves or bunches, it will be difficult to tack it afterwards.

Advice from a fairly recent convert to home sewing: Batting of any kind does need to be quilted, because it will clump and shift with wear and laundering, or even with gravity over time when hung in the closet. Tacking it to the shell and lining (rather than sewing through). as suggested by several folks above, is a good compromise, since machine sewing through all layers lets air through. Hand tacking is something you can do while watching TV or a movie!