Thermal Retention

This is the mechanism that makes peat therapy physically different from any other topical treatment. Unlike a cream, a serum, or even a hot bath — peat holds heat like nothing else. A peat pack at 42°C loses less than 1°C over a 20-minute treatment. Plain hot water drops 3.5°C in the same period (Korhonen 2008).

That’s not a small difference. It’s the difference between surface warmth that fades before your muscles relax, and deep, sustained heat that reaches joint capsules, deep muscle tissue, and subcutaneous layers. A single-site Finnish study found some peat-water mixtures more extreme still — they hadn’t started cooling at all after 30 minutes (Korhonen 2005).

How it works

The physics. Peat’s thermal retention comes from three properties working together. Its high water content gives it thermal mass. Its low thermal conductivity means heat transfers slowly to the surroundings. And the humin fraction — the insoluble organic matrix — acts as insulation, trapping heat within the peat structure. The result is a natural heat pack that maintains therapeutic temperature for an entire treatment session without reheating.

What sustained heat does to the body. When skin is held at 38–42°C for 20+ minutes, several things happen: blood vessels dilate, increasing circulation to the treated area. Muscles relax as sustained warmth reaches deeper tissue layers. Pain receptor sensitivity decreases. And — critically for peat therapy — skin permeability increases, allowing more of peat’s bioactive compounds to cross the skin barrier.

The synergy. This is why peat therapy is more than the sum of its parts. The heat enhances absorption of humic acids and fulvic acids, while those compounds provide anti-inflammatory and muscle-relaxing effects that heat alone cannot deliver. An RCT with 80 knee osteoarthritis patients demonstrated this directly: both peat packs and hot packs delivered the same temperature, but the peat group had significantly better outcomes (Evcik 2007). The heat was identical — the chemistry made the difference. A separate RCT comparing mature mud packs against a matched hot-pack control found the same pattern — mud outperformed heat alone on pain, function, and walking distance (Sarsan 2012).

Why it matters

Thermal retention is the cornerstone mechanism for:

• Joint inflammation — the condition with the strongest evidence for peat therapy. Sustained heat reaches joint capsules and periarticular tissue, while absorbed anti-inflammatory compounds reduce swelling. Multiple RCTs confirm this combination is superior to heat alone (Keilani 2025).
• Muscle pain — deep muscle relaxation requires sustained warmth that doesn’t fade after the first few minutes. Peat packs maintain this consistently (Korhonen 2008).
• Back pain — the paravertebral muscles along the spine need prolonged heat to truly release chronic tension. Peat mud packs outperform hot packs for spinal pain (Karaarslan 2022).

Thermal retention is less relevant for purely dermatological applications (face masks, peat cream) and is actually contraindicated for rosacea, where heat triggers vasodilation and worsens redness.

The evidence

Strong. The thermal properties of peat are well-characterised across multiple peat types — Korhonen (2008) tested peat from 17 Finnish mires and found consistent heat retention across all of them. The clinical superiority of peat over hot packs (same temperature, different medium) has been demonstrated in controlled trials for both knee and spinal conditions. This is one of the few peat mechanisms where the evidence is unambiguous: peat holds heat better than water, and the outcomes confirm that this matters clinically.