Water Proof Sample Envelopes. 3"x5" Sample envelopes great replacement for the traditional metal clasp. These envelopes can hold oil drenched (Invert) and water based samples without leaking or seeping through the envelope. They are also completely stamp able as well as can be written on just like a traditional envelope. They also fit in all traditional sample envelope shoe boxes. If you have any question call us @ 832.321.5153