The startled look in my wife’s eyes when I told her I had to sleep outside to test the Black Diamond Twilight Bivy, was priceless. She is used to the occasional backyard campout, but the 27 mph howling wind coupled with the drenching rain in the high 30s made her question my sanity. But I persevered and the four-season rating of the Twilight Bivy was put to the test.
This minimalist frameless bivy sack is a little over six-and-a-half feet long and over two-and-a-half feet wide. One tester reported that it was just big enough for his 6’ 200-pound frame, but for the average person, the fit of this sack is unrestrictive and you can even sit upright while cooking in the morning. Size note: A rectangular Big Agnes Air core fit inside nicely.
The bivy is basically polyester with a special water-resistant silicone nanocell treatment, that is lightweight, but still durable for its weight. (I won’t say waterproof because Black Diamond says it isn’t.) However, I awoke in a puddle after the storm, and was happy to find my down sleeping bag and body dry. And despite the 27 mph wind, I didn’t feel a draft. In later tests, it did just as well in the blowing snow.
Bugs are thwarted by the zippered mesh front that lies underneath the opening/entrance and loops on the outside to roll the screen up. With the bivy completely enclosed, there is no stuffy feeling thanks to the breathable NanoShield fabric which also doesn’t have the fragile feeling of other lightweight fabrics.
A long time ago, I got stuck in a bivy when the zippers malfunctioned (and my buddies still make fun of me for it). The zipper location on the Twilight is crystal clear and it unzips smoothly with a simple string. This is an important feature if the user hears rustling and doesn’t want to become a bear burrito (I’m guessing, here). I do wish there was some type of glow-in-the-dark bead attached to the zipper though (I’d like to see these on sleeping bags too!). The zipper goes across the shoulders, giving enough head room in the top of the bag to fit a pillow (or small dog). But, the Twilight packs down to less than a 16 oz. bottle, and a true minimalist probably wouldn’t pack a pillow that is bigger than their shelter anyway.
Bottom line: As an emergency bivy for a thru-hiker, or someone who wants to go ultra-minimal, this lightweight bivy sack will please and perform.