Flexible TPU is especially unforgiving about moisture. Bambu's product guidance for TPU 85A and 90A calls for drying before use and storing the material in a sealed container with desiccant below 20 percent relative humidity. For a blast drying oven, the listed condition is 70°C for eight hours; other supported drying hardware has different temperatures and durations. Those are material- and equipment-specific values, not a universal recipe for every TPU spool.
This matters once the foil package is opened. The packaging protects the filament during shipping, but the lasting storage system should be a resealable dry box or bag with fresh desiccant and, ideally, a small humidity indicator. The practical goal is to keep the filament dry between jobs rather than repeatedly rescuing a wet spool before every print.
Bambu also warns that its soft TPU 85A/90A grades are not compatible with standard AMS or AMS lite feeding. Check the exact filament grade and your H2D feeding path before attempting a multicolor or dual-material job. For soft TPU, conservative speed and a reliable feed path matter as much as moisture control. A clean storage setup is cheaper than troubleshooting bubbles, stringing and failed layers.