4" Width ProTapes Pro Gaff Premium Matte Cloth Gaffer's Tape With Rubber Adhesive, 11 mils Thick, 55 yds Length, White (Pack of 1)

I bought this gaffe tape because I thought the 11 mil thickness would make it more light-tight. However, you need 6 layers of it to even come close to that. $55 for a roll is quite a lot, but the 4 inch width is definitely nice. It's definitely sticky, sticks better than duct tape on metal surfaces, but it still rips paint and gypsum off drywall sometimes. I was using it to seal the corners of a darkroom which is painted white (The color of the room doesn't matter if it's actually dark and I like to be able to see when the lights are on) - but I really had to layer it on thick.