How to Use the UltraFlask Filter Cap for Trail Hydration
By HydraPak | Performance Hydration Reservoirs, Soft Flasks ... | Published: 2026-10-27
Category: How-to Guides
Learn how to use the HydraPak UltraFlask+ Filter Cap for quick, lightweight trail hydration. This guide covers setup, filtering, and maintenance steps.
Quick answer
The UltraFlask+ Filter Cap lets you drink freshly filtered water directly from streams and lakes by threading onto your HydraPak 42mm running flask. Here’s how to set it up, filter water, and keep it clean.
Why use a filter cap instead of a bottle filter?
The UltraFlask+ Filter Cap is designed specifically for runners and fastpackers who want to minimize weight and bulk. Unlike a separate filter bottle, this cap threads directly onto your existing HydraPak 42mm soft flask or handheld, turning it into a filtration system without adding extra gear. The trade-off is that it only works with 42mm threads, so it won’t fit standard wide-mouth bottles or reservoirs.
What the filter removes (and what it doesn’t)
According to HydraPak, the filter effectively removes common waterborne bacteria such as Giardia and Cryptosporidium. It does not remove viruses, heavy metals, or chemicals. For backcountry trips where viral contamination is a concern, you may need additional treatment like UV or chemical drops.
Step-by-step usage guide
- 1. Attach the cap to your flask: Unscrew the standard cap from your HydraPak 42mm flask and replace it with the UltraFlask+ Filter Cap. Hand-tighten until snug. Do not overtighten. Common mistake: cross-threading. Align the threads carefully before twisting.
- 2. Fill the flask with untreated water: Submerge the flask in a stream, lake, or other natural water source. Squeeze the flask gently to expel air, then release to draw water in through the filter. Avoid submerging the bite valve. Checkpoint: Do not fill from a source with visible sediment or algae—the filter may clog faster.
- 3. Drink through the bite valve: Bite down on the Blaster valve and suck to draw water through the filter. The valve opens only when bitten, so it won’t leak when not in use. Common mistake: biting too hard or not enough. A gentle bite is sufficient to open the valve.
- 4. Clean the filter after each use: Rinse the cap with clean water and backflush by squeezing clean water through the filter in reverse. Let it air dry completely before storing. Replace the filter according to HydraPak’s recommended lifespan. Checkpoint: Never store the cap wet—mold can grow inside the filter. Refer to the user manual for detailed cleaning instructions.
Product details
- UltraFlask™+ Filter Cap: Threads onto all HydraPak 42mm running flasks and handhelds. Features a traditional bite valve and high-flow Blaster valve. Effectively removes common waterborne bacteria. You can use your existing flask without buying a new bottle, and the bite valve lets you drink without stopping—ideal for trail runs.
UltraFlask™+ Filter Cap
