8 min read • July 2026
Fi Mini, Series 3, and 3+; what fits, what holds up, and the e-collar combo setup most guides never mention.
You dropped $150 on the Fi tracker. The band it ships with is fine for the suburbs. It’s not what active dogs, working dogs, or training dogs need for year-round use.
Most “Fi compatible collar” guides are product pages from one brand. They tell you their collar works with Fi, list the colors, and stop there. They don’t cover which Fi model you actually have — and that matters, because the collar attachment changed between generations. They don’t cover what happens when the collar absorbs moisture around a device you’re not removing every night. They definitely don’t cover how to run a Fi tracker and an e-collar on the same band.
That last one? Nobody covers it. This post does.
This matters before anything else. The collar attachment system changed between generations, and the Fi Mini uses a completely different method. Buying the wrong collar for your tracker is a frustrating $40 mistake.
Key takeaway:Series 3 and 3+ use the same end link, collars made for one work for both. Series 1&2 use an older connection. The Fi Mini uses no end links at all.
The Fi Mini comes with two versions of a universal strap. The strap slides on and holds the module to your collar band. For most everyday use this works well; but with heavy activity like swimming, hard running, or rough play, it’s possible for the module to slip out. If your dog is active, our TPU case is a more secure option: it holds the module in it’s own little box that slides onto a collar. It’s available in 3/4″ and 1″ widths.
Fi Series 3 and 3+ require a collar with Fi-specific metal end links sewn or screwed into the band. Without them, the module has nothing to clip into. The Fi Mini is different; its strap slides on and holds to any collar.
Your collar doesn’t need to be “Fi compatible” in the traditional sense. The Mini strap slides on and holds to any band … which means POP’s full color lineup is available to you.
Inline design: The end links are sewn or screwed directly into the collar band. The Fi module sits inline with the collar — flush with the band, low profile, clean look. The tracker sits on the outside of the collar and does not contact your dog’s neck.
On the collar design:Â Two small straps hold the Fi module on top of the collar band. The module never touches your dog’s skin. This design is slightly sturdier since there’s no direct pressure on the end links themselves.
There’s no Fi-specific width requirement; use the same width you’d choose for any collar. End links are sized to fit both standard widths.
Fi Mini note:Â The Mini’s strap slides on and holds to any collar width. For our TPU case, we offer a 3/4″ version and a 1″ version.
The module sits against the collar all day. If your dog swims, runs in rain, or works in the field, the collar is going to get wet. Leather absorbs that moisture and adds mold risk. The odor development isn’t just an annoyance; it’s happening right around your GPS hardware.
BioThane is non-porous. Water beads off. Mud sits on the surface until you wipe it off. No moisture accumulation around the module, no bacteria, no odor. A quick rinse and it’s clean.
You’re also not removing this collar every night … it’s the collar with the tracker on it. Low-maintenance isn’t a preference at that point, it’s a practical requirement. BioThane also stays flexible in cold weather when leather stiffens, which matters for hunting and field dogs in cold climates.
BioThane. The only collar material built for long-term wear with an electronic device.
Training dogs, hunting dogs, and field dogs often run two collar setups: the e-collar receiver on one band, a regular collar on another. Two bands, two sets of hardware, double the bulk on your dog’s neck. It’s not ideal for comfort, and it’s not ideal for working conditions.
Some of our collars are designed to accommodate both; one band that holds the e-collar receiver and the Fi GPS module together. Single collar. Both tools. No double-collar rig.
For this setup to work, your dog needs a large enough neck to comfortably fit a 4–5″ e-collar module, a 3″ Fi GPS module, and the hardware of the collar itself. It’s not right for every dog; but for the dogs that can run it, it’s the cleanest setup available.
The e-collar receiver sits against the collar constantly. Leather darkens and softens unevenly at the contact points and can grow mold in enclosed spaces. BioThane wipes clean in seconds; exactly why it’s already the universal standard in professional e-collar training.
Depends on the model. Fi Series 3 and 3+ require a collar with proprietary end links; they don’t work on standard collars. The Fi Mini is different: its universal strap slides on and holds to any collar or harness, so it works with any band you already own.
Series 3 and 3+ need collars with special end links sewn or screwed in … you have to buy a Fi-compatible collar. The Fi Mini uses a universal strap that slides on and holds to any collar or harness. If you have a Mini, any POP BioThane collar works.
Fi doesn’t have a specific width requirement. Use the width that fits your dog: 3/4″ for medium breeds and 1″ for large breeds over 50 lbs is common. The end links on Series 3/3+ compatible collars fit both widths. For the Fi Mini, our TPU case comes in a 3/4″ and a 1″ version.
Some of our collars are designed to accommodate both an e-collar receiver and a Fi GPS module on a single band. For this setup to work, your dog needs a large enough neck to fit a 4–5″ e-collar module, a 3″ Fi GPS module, and the collar hardware itself.
No. Series 3 and Series 3+ use the same end link style; a collar made for Series 3 works on 3+ and vice versa. The only consideration: if you want Fi’s behavior monitoring to work accurately on the 3+, Fi recommends an inline design rather than an on-the-collar design.
Yes! It’s the best option for an active or working dog wearing a GPS tracker. BioThane is non-porous, so water and bacteria don’t accumulate around the module. It requires no maintenance, stays flexible in cold weather, and outlasts alternatives by years. For a collar you’re not removing every night, that matters.
