Bend or Press?

A flex sensor measures how far a strip curves, so it tracks finger and joint angles. An FSR measures how hard a spot is pressed. Gloves and robot hands often use both: flex strips along the fingers, FSRs on the fingertips.

Length & Size

A 2.2″ flex strip covers one finger joint; a 4.5″ strip covers a whole finger, wrist or elbow. For FSRs, a 0.5″ round spot suits a fingertip button, a 1.5″ square catches presses that land anywhere on a pad.

Consistency

Branded Spectra Symbol strips (sold by SparkFun) are more consistent than unbranded clones. If you need five fingers to behave alike, either buy branded or buy a bulk pack and pick matched parts.

Interface

Bare sensors need one fixed resistor to form a voltage divider into an ADC pin. Module versions add the resistor (and sometimes an op-amp) on a small board, so you just wire VCC, GND and OUT.

Durability

Flex strips fatigue at the pin end, not along the strip. FSRs dislike sharp point loads and heat (never solder directly to the film tail). Choose crimp or clincher connectors for both.

Best Long-Throw Flex. A 4.5″ strip spans a whole finger, a wrist or an elbow, so it captures larger motions with a smoother signal than a 2.2″ part. The SparkFun 4.5″ listing currently has no featured offer on Amazon, so this Reland Sun 4.5″ version is the in-stock alternative. It wires exactly the same way (divider resistor into an ADC pin), and the seller notes the same handling rule: the printed side goes on the inside of the bend and the pin end must never flex.

Best Plug-and-Play. This kit pairs an FSR402 with a small linear voltage conversion module and a connecting cable, so instead of building a divider you wire VCC, GND and the analog output straight to your board. The module works from 3.3 V or 5 V, which makes it a clean fit for ESP32 and Raspberry Pi Pico boards as well as classic Arduinos. The conversion stage also gives a more usable output swing than a bare divider, which helps beginners and classroom builds where nobody wants to tune resistor values.

Best Bulk Pack. A two-handed glove needs ten flex sensors, a robotic hand needs five, and a classroom needs dozens. This Wuden 10-pack of 2.2″ strips is the economical way there. Clone strips show more part-to-part spread than SparkFun’s, so measure each one flat and fully bent and store per-finger calibration in firmware. Having spares on hand is also the cheapest insurance against the pin-end failures every flex project eventually hits.

Best Long-Lead FSR. The standard FSR402 tail is short, which is awkward when the sensing pad sits on a fingertip and the electronics sit on the back of the hand. This Walfront long-tail version keeps the 0.5″ round sensing area and 0–10 kg range but extends the printed lead, so you can route the connection away from the contact point without splicing. With dozens of reviews it’s also one of the better-tested generic FSR402 listings on Amazon right now.

Best Large-Area Pad. When you can’t predict exactly where a press will land, a bigger target beats a sensitive one. This FSR406-style square pad gives you roughly 1.5″ of sensing area with the same ~100 g–10 kg range and two-wire readout as the FSR402. It’s the right choice for footstep pads, seat occupancy, DIY dance-mat tiles and palm-sized touch surfaces. Genuine Interlink and Adafruit square FSRs are currently unavailable on Amazon, so this generic version is what we’d buy today.

Best High Range. Standard FSRs flatten out around 10 kg, which is useless for a seat, a bed or a person standing on a pad. The MD30-60 stretches the range to roughly 30 kg on a 30 mm round head that is under 0.6 mm thick, with a sealed, water-resistant sensing area and a rated life of over a million presses. Like every FSR its curve is steep at low force and flattens near the top, so drop the divider resistor (for example 1 kΩ instead of 10 kΩ) when you care about the heavy end.

Building a gesture glove?

Use the SparkFun Flex 2.2″ on each finger for the most consistent readings, or the Wuden 10-pack if budget matters and you’ll calibrate per finger.

Robot hand with grip feedback?

Flex strips for joint angle plus a long-tail FSR402 on each fingertip, so the lead runs back to the palm cleanly.

Pressure-sensitive button?

The DIYables FSR402 and one 10 kΩ resistor. Prefer no resistor maths? Take the DAOKAI module kit.

Tracking wrist, elbow or knee?

Go long: the 4.5″ flex sensor spans the whole joint and gives a smoother signal.

Footsteps, mats or seats?

The FSR406 square pad for light loads, the MD30-60 when a person’s weight is involved.

Need real grams?

None of these. Use a strain-gauge load cell; see our load cell & HX711 guide.

What’s the difference between a flex sensor and an FSR402?

A flex sensor responds to bending: its resistance goes up as the strip curves, so it measures angle. An FSR402 responds to pressing: its resistance goes down as force increases, so it measures how hard something pushes on it. A flex sensor pressed flat barely changes, and an FSR bent without pressure gives unreliable readings, so pick the one that matches the motion you want to sense.

What resistor should I use with a flex sensor?

Wire the flex sensor and a fixed resistor in series between VCC and GND and read the midpoint on an analog pin. For a 2.2″ strip that runs from about 25 kΩ flat to roughly 100 kΩ bent, a 47 kΩ resistor gives a good swing. Record the ADC value flat and fully bent for each sensor, then use map() to convert readings to an angle. Our FSR with Arduino tutorial walks through the same divider approach for force sensors.

Do these sensors work with ESP32 and Raspberry Pi?

Yes with ESP32, Pico and any board that has an ADC: power the divider from 3.3 V instead of 5 V. On ESP32, prefer ADC1 pins (ADC2 is unavailable while Wi-Fi is on) and expect some non-linearity near the rails. A standard Raspberry Pi has no analog inputs, so add an external ADC such as the MCP3008 or ADS1115.

Why do flex sensors break, and how do I stop it?

They almost always fail where the strip meets the metal pins, because repeated flexing there cracks the printed traces. Glue or clamp the pin end to something rigid so all the bending happens along the strip, add heat-shrink strain relief over the joint, bend over a curve rather than a sharp fold, and avoid soldering directly onto the pins with a hot iron. Buying a spare or two is cheap insurance.

Can an FSR402 measure weight accurately?

No. FSRs have wide part-to-part tolerance, a curved response and creep under constant load, so they are great for “pressed or not, and roughly how hard” but poor for grams. Placing a small rigid puck over the active area improves repeatability, but for a scale, a tension gauge or closed-loop force control, use a strain-gauge load cell with an HX711 amplifier.