There are basically two types of auto racing suits: single-layer and multi-layer. In addition, you have one or two piece auto racing suits. We recommend that drivers wear one-piece suits, and crewmen can choose from from either type depending upon their responsibities.
While racing suits are most commonly identified by their SFI or FIA ratings, the TPP rating is the best measure of a particular racing suits protection level. TPP ratings are an indication of how long a suit will protect you before you would incur a second degree burn. The TPP rating is divided in half to determine the number of seconds until the human tissue reaches a second-degree burn. For example, if a particular fabric has a TPP rating of 35, it takes 17.5 seconds until a second-degree burn occurs in a flashover situation.
The TPP rating is calculated from a mathematical formula that relates the heat transferred through the garment material to the amount of energy that would be required to cause a second degree burn. TPP results are typically reported as a rating. The TPP rating is the time to incur a second degree burn multiplied by the heat exposure level that the material is exposed. The higher the garment TPP rating, the more time that is required before a second degree burn will occur. The chart below outlines the SFI ratings based on TPP results (shown to the right of the slash mark on the driver suit patch) with the corresponding times to a second degree burn:
| SFI Rating | SFI Name | TPP Rating | Time to 2nd Degree Burn | Comments |
| SFI 3.2A/1 | SFI-1 | TPP 6 | 3 Seconds | Common Single Layer Suit |
| SFI 3.2A/5 | SFI-5 | TPP 20 | 10 Seconds | Common Multi-Layer Suit |
| SFI 3.2A/15 | SFI-15 | TPP 38 | 19 Seconds | Used for Drag Racing Applications |
| SFI 3.2A/20 | SFI-20 | TPP 80 | 40 Seconds | Used for Top Fuel Drag Racing |
TPP rating can vary within an SFI Rating, for example SFI 3.2A/5 rated suits (commonly called SFI-5) are available with TPP ratings anywhere from 19 to 26 depending on the number of layers and the fire-retardant material used to construct the suit. The only way to increase a TPP rating is through adding multiple layers. However, as you increase layers, suits get bulkier, and bulk does not equal comfort. Your goal in selecting a firesuit should be the balance of comfort with maximum protection.
The easiest and best way to to increase TPP is to wear fire retardant underwear under you firesuit. These garments are typically made of Nomex, CarbonX or other fire-resistant (FR) materials. It is highly recommended that any driver wear fire-retardant underwear to improve TPP and better protect against injury.
