But even something so simple and cheap as a 55 gallon yellow trash bag stashed in a pocket. You can blow it up and tie closed with a string while also attached to a D-ring is extremely effective at being seen 5 - 10 miles away and at night with a light glowing inside.
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. I have a couple of extra sealed bags. If you want one, PM me a mailing address (work,home,po box,etc) and I'll send it to you free. If it adds just one additional layer of safety, & confidence it's worth it to bring on dives.