I have a jungle blanket, and find it fine. It is however, nowhere near the weight you're requesting. 400 grams is ~14oz. The jungle blanket is somewhere on the order of 26oz (~700 grams).
If my math is right though, a DIY 2.5oz apex blanket would be in that weight range, depending on exact size and fabric used. I did the math for a 72in by 58in (2yd long, by the usable width of apex and most fabric), and .9oz/sq yd fabric. The total was 13.8oz (391oz). If you did a tapered blanket, you could shave off quite a bit. Same thing with some of the crazy light fabrics.
Good luck finding something you're interested in .
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