People can intentionally or unintentionally transport seed of a diversity of species over long distances, facilitating plant invasions. To better understand factors affecting unintentional human-mediated seed dispersal, we quantified the effects of seed traits and fabric type on the retention potential of weed seed on clothing. First, we compared seed retention among 33 species of weeds that differ in seed morphology using three fabrics. We then compared seed retention for 10 different fabrics using seed from five species of weeds. Retention potential, calculated as the percentage seed retained on fabric after shaking for fixed periods of time, was compared using Linear Mixed Models. Across the 33 species, seed of most species fell off fabric soon after shaking commenced: 17 species had low retention potentials (<20% of the seed remain attached after 5 min of shaking), 10 species had moderate seed retention (20–50% seed retained), and only five species had high retention potentials (>50% seed retained). Retention potentials varied among fabrics, with seed more tightly attaching to fabrics with “woolly” or “fleecy” characteristics such as fleece, knitted wool, double weave wool nylon blend (hiking socks) and ribbed cotton/nylon (sports socks), than to smoother fabrics such as canvas, fine nylon weave, denim and drill cotton. The weight, length and presence of attachment structures affected how long seed remain attached. The effect of these traits varied among fabrics. Seed with structures such as hairs, awns and pappus remained attached for longer on fabrics like fleece and wool, but not on smoother fabrics. These results support the observation that people wearing clothing made of different fabrics are likely to disperse different combinations of weed seed, depending, at least in part, on seed traits. Unintentional human mediated seed dispersal via clothing is therefore a very selective example of epizoochory favouring some weeds more than others.