Tube-type water pipe insulation questions

As commonly available in the stores, these tubes seem to be made of 2 different types of foam, one that is slightly more "rubbery" than the other. This link says that one is used for copper, the other for galvanized steel, but it doesn't say which type is for which kind of pipe: http://frentzandsons.com/content/howto/sweatingcopperpipes.htm
Also, what size should the tube be -- just enough to fit over the pipe, or slightly larger so that there's some sort of an "air gap" between the tube and the pipe?
Thank you.
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The closed cell provides more insulation value. A lot harder to find as it is a lot more expensive. Get the size for your pipe, snug fit. Then use plenty of duct tape to hold it on. I use only the metal tape as the other stuff releases in a couple of years from the heat. A good razor knife and your good to go
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Thx for comment on sizing. And yes, there is a significant price difference. Would Nashua #345, "Industrial Grade HVAC Duct Tape" be a good one to use?
SQLit wrote:

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Just a practical matter. I have seen proposals that suggest that insulating more than the first 10 feet becomes a deminishing returns sort of thing. I do 20 feet and stop.

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Everything has a law of diminshing return, but true energy efficiency can not be acheived with out the extra cost. Payback will be evident and real as I took out a Electric Rheem with a blanket an went fron 30 $ to 6 $. Yes electric is double the cost but my sawings exceded that.
Insulate all pipes of hot water , use closed cell foam the type that has glue strips installed so taping is not necessary. Doubling insulation is not a bad idea since 1/3 of gas costs can be heating water.
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Tubes are obsolete. I suggest you switch to a transistorized model.
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Axial wrote:

Update: I bought both to try, but ended up preferring the "rubbery" type of insulation (it's similar to neoprene; one brand is Rubatex) rather than standard foam. Pricing for self-sealing type: standard foam 99 cents / 6ft, rubber-type 3.49/6ft.
The rubber-type was much easier to install. It stretched around elbows so it didn't need cutting, and could easily go around "T"s. It was much easier to fit around multiple short-segmented areas like up to the bathroom sinks.
Thx to responders for advice.
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