This thing is great! Read further:)

155mm tall x 54mm wide square tub with 2mm thick walls. Print tube with PLA and bottom plug with TPU 85A recommended. Wrap square tube with 1" dense foam insulation on all 4 sides and bottom (pink foam is far more dense than white styro). Tape foam box and leave top open (I used Pella Window tape which has aluminum exterior and rubber like glue on back so the foam contraption was waterproof).

Fill with room temp to warm tap water and this mold will freeze the ice from the top to the bottom. This is called directional freezing and the ice will be extremely clear at the top and the bottom will be cloudy and/or will not freeze after about 24 hours. Reason for this is once the water freezes about 4" down the tube (which is just over 6" tall) all of the impurities and air bubbles get pushed to the bottom 2" of the ice tube during top to bottom freeze process. From there, you cut the bottom end off the 2" wide 6" long cube and split the other 4" long cube in 1/2 to have two 2" cubes, perfectly clear (for the most part:)

TPU plug is used to remove after freeze and push ice out when the walls thaw a little and the ice shrinks enough to push through the tube. Use food safe plastic when printing this if you plan to use the ice for drinks.

I also added a 2 cube freezer tray. I use this to put the cubes in after cutting when the cubes are wet from handling. They sit in the tray, re-freeze and then you can put in bag or tray and they will not stick together. Print this with no bottom layers and 9% infill. This is helpful if water penetrates the TPU filament and can drain out the bottom and dry off. Good idea to print the rubber bottom the same way, cubic infill pattern.

Also including hex version that should be able to fit into the same foam contraption you build for the square tube. This may not work as well since cold air will get down the side walls of the hex tube but may be worth a shot. Or just make a foam hex cooler to accept this mold.