It's not quite the fibre that the original is, but the alpaca/silk blend seems like it might get saggy. I'm lying, my real reason for not going with the alpaca/silk blend is because this is an experiment and the alpaca/silk bumped up the cost of the experiment substantially. This way, if the whole thing refuses to come together, I'll have only wasted $30 and tons of my time, instead of $60 and tons of my time. If it goes well, I might knit one in black in the alpaca/silk, and compare. Hey, you gotta dream. 
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I'm going to a wedding this afternoon (well, when I started writing this blog post it was Saturday- so bear with me on the timeline), and was naturally rushing around yesterday to buy a wedding gift for the happy couple. I had it in my head that a lovely throw blanket from Pottery Barn would be good, but I became disgusted when I saw these:

And they were retailing for $115 (CAD), which is beyond ridiculous. By the way, I checked it out on their website- it's %100 acrylic. What the muffin are they thinking?!
I realize that I now need to approach the announcement of every event that I know I'll be bringing a gift to with the question: 'what can I knit for this?' I'm kicking myself for not thinking about knitting an afghan for Steph and Steve ages ago, when the engagement announcement went out. Instead, I went to Williams Sonoma and spent waaaay too much money on very fancy Peugeot salt and pepper grinders. I find myself hoping against hope that they'll return them, and realize that the amount of money that I spent on them is indicative of how stupid I felt for not starting on knitting them an afghan.