HydraPak 42mm Filter Cap — Threaded Bottle Filter for Seeker & Flux, Lightweight High‑Flow Microbial Protection

The HydraPak 42mm Filter Cap is a lightweight, threaded water filtration accessory that turns any compatible 42mm HydraPak bottle into a high-flow, microbiologically rated drinking system.

Designed for runners, cyclists and backcountry travelers, this compact filter screws onto all HydraPak products with a 42mm opening — including running flasks, Seeker bottles and Flux bottles — to provide on-demand filtered water without carrying bulky equipment. At just 57 grams and 129 mm long, it balances low weight with a durable hollow-fiber membrane that meets EPA and NSF testing guidelines for common contaminants.

How effective is this filter at removing contaminants?

The HydraPak 42mm Filter Cap uses a hollow fiber membrane and has been tested to remove common bacteria and parasitic cysts to high-efficiency levels per EPA guide standards and NSF testing protocols. It also reduces microplastics sized 3.0 microns and larger as validated to NSF 42.

• Removes E. coli and many bacteria at 99.9999% per EPA guide standards.
• Removes parasitic cysts at 99.999% per EPA and NSF P231 guidance.
• Reduces microplastics ≥3.0 microns at 99.999% per NSF 42 testing.
• EPA company and establishment number: 102123 for traceability.

What performance can I expect in the field?

This filter delivers a high flow rate that supports active use: you can access potable water quickly without long pumping cycles. It’s rated to filter approximately 1,500 liters and generally produces water at a rate greater than 1 liter per minute under typical use.

• High flow: >1 L/min for fast refills and quick sips on the move.
• Service life: roughly 1,500 liters of fresh water before replacement.
• Lightweight: 57 g (2.0 oz) minimizes pack or pocket bulk.
• Compact length: 129 mm (5.1 in) fits neatly on running flasks and bottles.

How do I use and care for the 42mm Filter Cap?

Thread the filter onto any HydraPak product with a 42mm opening and open the high-flow nozzle to drink. Keep the dust cover closed when not in use, and avoid freezing the filter — freezing can damage the hollow fiber membrane and reduce effectiveness.

• One-handed operation: easy open/lock high-flow drink nozzle with dust cover.
• Storage: keep dry and avoid freezing temperatures to protect the membrane.
• Cleaning: follow manufacturer directions for backflushing or rinsing when flow slows.
• Compatibility: fits all HydraPak 42mm threaded products like Seeker and Flux.

Will this fit my current HydraPak bottle or flask?

If your HydraPak product has a 42mm opening, the filter cap will thread on directly and form a secure, drinking-ready connection. It’s built specifically to mate with HydraPak running flasks, Seekers and Flux bottles that use the same 42mm thread standard.

• Thread size: 42mm (1.65 in) diameter for direct compatibility.
• Works with: HydraPak running flasks, Seeker series, and Flux bottles.
• Weight and length: integrates without adding significant bulk or changing carry ergonomics.

Who this is for: The HydraPak 42mm Filter Cap is aimed at trail runners, cyclists, hikers and minimalists who want fast-access filtered water without carrying a heavy purifier. It’s ideal for anyone who uses HydraPak 42mm bottles and flasks and needs a reliable, lightweight filtration solution for day trips, ultraruns, bikepacking or backcountry outings. Avoid using in freezing conditions and follow care instructions to maximize filter life.