The set up..

Groups of hamsters were placed in cages with controlled one-way air flow. There were three pairs of cages; each pair consisting of adjacent cages A (COVID-infect hamsters) and B (non-infected) with air flowing in one direction (from A to B). Pair 1 had a "mask" on A and not on B. Pair 2 had a "mask" on B but not A Pair 3 had no "mask" on either

Pair 1: When mask is worn by the infected

The adjacent cage  had  a15% infection rate

Pair 2: When mask is worn by the uninfected

The adjacent cage  had  a 33% infection rate

Pair 3: When mask is worn by the none

The adjacent cage  had  a 66% infection rate

Conclusions..

1. Masks protect others 2. Masks offer some degree of protection to the wearer

Reusable face masks and face mask filters for Canadians