Or sign in with:
| Size | US | Chest | Waist | Hip |
|---|---|---|---|---|
| XS | 2 | 32 | 24 - 25 | 33 - 34 |
| S | 4 | 34 - 35 | 26 - 27 | 35 - 26 |
| M | 6 | 36 - 37 | 28 - 29 | 38 - 40 |
| L | 8 | 38 - 29 | 30 - 31 | 42 - 44 |
| XL | 10 | 40 - 41 | 32 - 33 | 45 - 47 |
| XXL | 12 | 42 - 43 | 34 - 35 | 48 - 50 |
Thermal Protective Performance — what the number actually measures, why two SFI 3.2A/5 suits can have wildly different TPP scores, and how to read TPP when comparing racing suits.
The hidden number behind every SFI rating, broken down for racers who want to know what's really protecting them.
Every racing suit has an SFI rating. SFI 3.2A/1. SFI 3.2A/5. SFI 3.2A/15. Most racers know what these mean: higher number, more protection. What most racers don't know — including some sanctioning body tech inspectors — is that the SFI number isn't actually the measurement. It's a classification tier based on another number called TPP, or Thermal Protective Performance. TPP is what's really being tested. SFI is just the label.
This matters because two suits with the same SFI rating can have meaningfully different TPP scores — and therefore meaningfully different real-world protection. This guide explains exactly what TPP measures, how it's calculated, why it varies within an SFI tier, and what to look for when comparing racing suits at the spec-sheet level. If you've already read our SFI Ratings Explained guide, this is the next layer down — what's inside that label.
Thermal Protective Performance is a laboratory measurement of how long a fabric or garment can protect human skin from second-degree burns when exposed to a controlled heat source. The test was originally developed for firefighter turnout gear in the 1970s and adopted by the SFI Foundation for motorsport applications shortly after.
Here's the test, simplified:
A TPP of 6 means roughly 3 seconds of protection. A TPP of 20 means roughly 10 seconds. Higher TPP = more time before serious injury.
Three seconds doesn't sound like much. But in a real cockpit fire, three seconds is the difference between getting your harness off and not. SFI 3.2A/1 with TPP 6 has saved racers' lives. SFI 3.2A/5 with TPP 20 has saved many more.
SFI ratings are tiers. TPP is the underlying score. The SFI Foundation sets a minimum TPP for each tier:
Here's the key point most racers miss: these are minimums, not exact values. A suit can be SFI 3.2A/5 certified with a TPP score of 19, 22, 25, or even higher. The SFI tier is the floor; the actual TPP can be anywhere above it.
Three factors drive how much TPP a suit actually delivers above its SFI minimum:
This is why a $300 SFI 3.2A/5 suit and a $1,500 SFI 3.2A/5 suit are not the same product. The SFI label confirms both meet the minimum. The TPP score — when manufacturers publish it — tells you which one over-performs.
Buyer Tip
When comparing suits at the same SFI rating, ask the manufacturer for the actual TPP score. If they can't or won't tell you, the suit probably just clears the minimum.
TPP needed for survival depends on fire risk — fuel type, fuel quantity, cockpit enclosure, and how long it takes to bail out. Practical TPP recommendations by discipline:
For the full SFI rating breakdown by series and class, see our rating-by-discipline guide.
Most retailers list only the SFI rating. The actual TPP value is usually buried in the manufacturer's spec sheet or test report. Three places to check:
The TPP a suit has on day one is not the TPP it has after a season of racing. Real-world TPP drops because of:
A 5-year-old suit with a valid SFI label still passes tech. Whether it still has its original TPP is a different question. If your suit has seen heavy use or contamination, the certification date doesn't tell the whole story.
The FIA 8856-2018 standard — the international equivalent used by World Endurance Championship, IMSA, and SRO series — measures protection slightly differently than SFI. The FIA standard requires roughly TPP 35+ for compliance (in their HTI methodology, equivalent to about 12 seconds of protection), with the 2026 update increasing this from the previous 11-second standard.
Rough equivalence:
For amateur endurance racers comparing SFI vs FIA, see our endurance racing suit guide.
This guide draws on the following authoritative sources. Always verify against the current versions of these standards before competing:
Keep going — more racing-suit guides from the HS Race Gear blog.
Which SFI rating each dirt oval body requires, by class. Street stock through winged sprint car, plus what tech actually checks.
SFI 3.2A is tiered and US-focused; FIA 8856-2018 is single pass/fail and international. Why one won't reliably substitute for the other.
CIK Level 1 vs 2, junior fit and growth room, senior sponsor placement, shifter-specific upgrades, and WKA/SKUSA/Rotax requirements.
Every HS Race Gear custom suit ships with full documentation — SFI rating, TPP score, material breakdown, manufacture date. Built with genuine Nomex® for higher TPP at the same SFI tier. Starting at $329. Free shipping on custom suits.
