This is a continuation of a long topic, addressed by post number rather than by page. Start at post 1.
Post #88 answers the question as asked. The question underneath it is different.
A phase-change pack holds a defined temperature while it changes state and then behaves like anything else. A gel pack starts cold and warms continuously. They are different tools for different transit lengths.
I am confident about the direction and much less about the magnitude.
Temperature loggers in the parcel exist and are occasionally used for high-value shipments. They are the only thing that turns an argument about transit into a record.
If that is already documented somewhere, ignore me and link it.
Arrival condition tells you about the last few hours and very little about the middle of the journey. A pack that is soft on arrival may have been soft for four days or for four hours.
Post #92 is right about the mechanism and I think understates the practical bit.
I would keep Domestic fridge temperature mapping and the decision it usually gets used for separate in this thread. They are related and they are not the same question, and merging them is why the last one went badly.
Coming back to post #95, because the follow-up matters more than the original answer.
A temperature indicator that has tripped tells you a threshold was crossed. It does not tell you for how long, and duration is most of what determines whether anything happened.
The disagreement above is smaller than it looks once the terms are fixed.
Two questions I would want answered before drawing anything from the Domestic fridge temperature mapping data above: how were the cases selected, and what happened to the ones that dropped out.
Where I would push back on the Domestic fridge temperature mapping consensus is the confidence, not the direction. The direction looks right. The confidence is borrowed.
I had written a reply contradicting post #98 and deleted it. Here is what survived.
Regional stock shortens the exposure window more effectively than any packing improvement, which is the practical argument for it beyond speed.
Domestic refrigeration: most lyophilised peptides are stored at 2–8 °C (35–46 °F). That is standard refrigerator temperature. Check your refrigerator's actual temperature; some are warmer than the label.
A guess, clearly labelled as one.
Answering the question post #100 raises rather than the one it answers.
Temperature excursions: brief excursions above 8 °C are tolerable for most compounds. Hours to a day at room temperature is usually acceptable. Days to weeks at room temperature risks degradation.
Happy to be corrected if someone holds better data than mine.
Lyophilised material is far more tolerant of a warm transit than a solution would be, which is why suppliers ship dry and why an excursion is not automatically a loss.
Shipment during summer or to hot climates: consider shipping to a cold-storage facility rather than to home if temperatures will be high. Alternatively, time shipment to arrive when you can refrigerate immediately.
Temperature logging: devices that record temperature over time let you confirm cold chain was maintained. Useful if a shipment was delayed or if you are concerned about excursion.
For what it is worth, the same held on the two occasions I checked.
Building on post #106 rather than restating it.
Repacking cold material into a domestic refrigerator promptly on arrival is the one step that is entirely within your control and the one most often delayed.
Post #106 answers the question as asked. The question underneath it is different.
An honest declaration on Domestic fridge temperature mapping: I have a prior here and it is strong enough that you should weight what I say downward. Stating it rather than hiding it.
Helpful, and short, which on this subject is harder than long.
Confirming post #112 from a second method, which matters more than confirming it from a second person.
The honest summary: pack quality is visible, transit history is not, and only the second determines what happened to the material.
Post #112 describes the usual case. This is about the unusual one.
I have three months of notes on Domestic fridge temperature mapping and the honest summary is that the trend is real and the week-to-week numbers are noise. I nearly drew the opposite conclusion from the first fortnight.
Adding the measurement that post #115 says would settle it.
A note on how Domestic fridge temperature mapping gets discussed rather than on Domestic fridge temperature mapping itself: the confident posts get the replies and the careful ones get ignored, and the careful ones have been right more often.
Freeze-thaw: some peptides tolerate freezing; others do not. Check your compound's labelling. Generally, repeated freeze-thaw is worse than single freeze-thaw.
Noting that I have skin in this question and have tried to discount for it.
Something worth flagging about Domestic fridge temperature mapping: the strongest-sounding claims in this thread are the ones with no source attached, which is the usual pattern and not a coincidence.
Reframing Domestic fridge temperature mapping slightly, because I think the disagreement is about the question rather than the answer. If the question is "does it happen", yes. If it is "how often", nobody here knows.