I'm not sure why Aurifil uses nylon either (though I'm sure they have some good reason). They do have an ironing guide for working with their mono threads:
[h=5]Ironing Guide[/h]
<section class="av_textblock_section" itemscope="itemscope" itemtype="http://schema.org/CreativeWork"> 150 c° – 302 F° Optimum Temperature. While protecting your stitches from the hot plate with a cloth.
160 c° – 320 F° At this temperature the thread will start to shrink by 2%
+240 c° – 464 F° At this temperature the thread will start to melt
I guess that makes sense. Thread is a fiber. We wouldn't iron nylon or polyester fabric on the Cotton setting, so I guess it's only logical that the thread would also take a lower setting. I looked it up & most irons hit 150C on the cotton/poly blend setting.
Honestly, though, once I've quilted it, I don't press my quilts anyways.
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