Can lyophilized peptides survive a few days at room temperature in transit?

Generally yes. A few days at room temperature in transit is the normal, expected condition for a dry (lyophilized) peptide. Bachem's handling guidance states peptides may be shipped at room temperature even though cold storage is preferred for long keeping. This is why suppliers routinely ship lyophilized powder without ice and ask you to refrigerate or freeze it on arrival. The bigger risk in transit is usually moisture, not the few days of warmth. A cracked or loosened seal lets the powder pull water from the air, which lowers content and can speed degradation. Sustained heat well above 30 to 40 C, or peptides rich in oxidation-prone residues (Cys, Met, Trp), shorten that safety margin. What's less certain is any single product's exact tolerance. Stability is sequence-specific, so treat "a few days warm" as fine for most, but check the supplier's own storage sheet. This is research-use information, not medical or dosing advice.