The 425 seems to have higher steel adhesion and tensile strength. 3340 looks to be specifically geared towards HVAC. Here’s a pdf to help select metal tapes:

The 425 seems to have higher steel adhesion and tensile strength. 3340 looks to be specifically geared towards HVAC. Here’s a pdf to help select metal tapes: https://multimedia.3m.com/mws/media/856073O/3m-metal-foil-tapes-brochure-6-2012-high-resolution.pdf https://multimedia.3m.com/mws/media/856073O/3m-metal-foil-ta... And the data sheets for both tapes: https://technicaldatasheets.3m.com/en_US?pif=000010?locale=en-US https://technicaldatasheets.3m.com/en_US?pif=000010?locale=e... https://technicaldatasheets.3m.com/en_US?pif=000116?locale=en-US https://technicaldatasheets.3m.com/en_US?pif=000116?locale=e... And some more tape pdfs, honestly a lot of it is super interesting, I never put much thought just into how many different kinds of adhesives there are: https://multimedia.3m.com/mws/media/1016166O/3m-masking-and-surface-protection-products.pdf https://multimedia.3m.com/mws/media/1016166O/3m-masking-and-... https://multimedia.3m.com/mws/media/1015901O/3m-industrial-adhesives-and-tapes.pdf https://multimedia.3m.com/mws/media/1015901O/3m-industrial-a... https://multimedia.3m.com/mws/media/1012104O/3m-converter-markets-selection-guide.pdf https://multimedia.3m.com/mws/media/1012104O/3m-converter-ma...