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2 layer racing suit vs. 1 layer and underwear?

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Be prepared for more info than you ever wanted to know....

Ok neither..or both IMO as a firefighter for 32 years (who has been on fire) and a fromer SCCA competitor I would forget all about the single layer..double layer underwear stuff and just go strictly by the rating. You are looking for an "exceeds"SFI-3.2A/5 suit, you can get them in pants/ jacket or one piece. I prefer the one piece as you can just roll down the top and tie it around your waist. The jacket version is actually more convenient but if you do get into a fire and you're trying to get out of the car (lie a window, or crawl across to the other side to escape) the jacket/ pant can separate around the waist and you can get exposure. You can obtain the SFI 3.2A/5 rating with a single layer suit and underwear but the problem with that is in my experience the underwear is kind of a PITA because it wants to roll up inside the suit and is basically another set of garments that have to be maintained. I prefer to just put the suit on a forget it. Don't forget socks, gloves and a balaclava as well.
Here is a website for decently priced suits, I would shy away from their helmets however, Bell or Simpson is a much better (quality and design) piece than the G-Force stuff.

IMO stay away from the "pyrovatex" it doesn't wear well.

You also need to pay attention to the TPP rating, (basically when YOU start to melt) not all SFI3.2/5 ratings are the same.
I stole this from another website because I could not explain it any better.

TPP (Thermal Protection Performance) testing shows CoolTek FR apparel outperforms conventional fire protection products by as much as 70%


The Speed Equipment Manufacturers Association (SEMA) was formed in 1963 with the central purpose of developing of product specifications for the suppliers of equipment used in racing. SEMA later formed SEMA Foundation, Inc. (SFI), to organize and manage an expanded industry specification program. The name was shortened to SFI Foundation, Inc.(Main)

One of SFI standards (3.2a) is a specification for racing car driver garments that includes tests for measuring garment material flame resistance, heat resistance, and thermal insulation (based on Thermal Protective Performance or TPP testing). The specification contains a rating system based on the garment's TPP test results. The TPP test evaluates the garment material’s thermal insulation in the presence of both direct flame and radiant heat. The purpose of the TPP is to measure the length of time that the person wearing the garment can be exposed to a heat source before incurring a second degree, or skin blistering, burn.

TPP results are reported as a time-to-second degree burn. This result is derived from a complex mathematical formula that related the heat transferred through the garment material to the amount of energy that would be required to cause a second degree burn. TPP results may also be reported as a rating. This rating is the time-to-second degree burn multiplied to the heat exposure level that the material is exposed to (usually 2.0 calories per square centimeter per minute – equivalent to a fireball). The higher the garment TPP rating, the more time that is required before a second degree burn will occur. Below are 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
TPP Rating
Time to 2nd Degree Burn

3 Seconds

7 Seconds

10 Seconds

19 Seconds

30 Seconds

40 Seconds

A common misunderstanding about SFI ratings is that they represent the number of fabric layers in the garment. It is actually possible for driver suits with differing numbers of layers to have the same performance rating. This is due to the wide range of materials used by manufacturers today.

This standard sets out that a TPP rating of 80 is required for suits worn by top fuel drag racers. By contrast a TPP rating of 38 is required for NASCAR events. Other standards bodies also rely on TPP ratings; for example A TPP rating of 35 is required for structural fire fighting protective clothing to meet National Fire Protection Association (NFPA) standards.

We have now done two rounds of fire resistant testing at Intertech Testing Services (ITS). In each round of testing, Hydroweave fabric (of which CoolTek products are made) was tested using an aramid fiber (Nomex) version of our product with a 4.5 oz shell fabric. The first tests were conducted dry and then a second set of tests was conducted wet (with the material activated).

The normal test time is 35 seconds long (equivalent to a maximum TPP rating of 70), but longer test times are possible as long as the material remains intact and there is no danger of damage to the equipment. In addition to time-to-second-degree burn and TPP ratings, the ITS data showed measurements of time-to-pain. Time-to-pain is a measurement of the time required for the heat transfer through the material to cause pain sensation. This occurs when the skin itself reaches roughly 111 degrees F (44 deg C).

In our dry tests, the average time-to-pain for Hydroweave was 11.8 seconds with a time-to-burn of 27.1 seconds. When tested wet (activated), we had time-to-pain of >35 seconds. In effect, the full 35 second test time had elapsed without recording a time-to-burn. The increased wet performance did not necessarily mean that the time-to-burn would be 3 times longer than the dry times, but it suggested that the TPP rating (which relies on a number of factors) would be much longer than values produced by the standard 35 minute test.

An additional series of tests were run with the TPP apparatus set up to run out to 50 seconds. This testing showed similar time-to-pain measurements (at approximately 35-37 seconds, but a time-to-burn was not measured within the 50 second exposure period. This indicates that this material system had a TPP rating of over 100; however, we are unsure how far the TPP rating for this system would be beyond 100.

In addition to TPP testing, we have also had ITS perform radiant heat tests. This involved similar testing as in TPP tests, but materials were oriented vertically instead of horizontally, and specimens were exposed to a lower heat flux of 0.1 calories per square centimeter per second (1/20 the heat level of the TPP exposure). In these tests, the rise time to 19 C is equivalent to the time-to-pain in the TPP tests. The rise time to 31 C is the equivalent to time-to-burn in the TPP tests. We used this measure because the Stoll curve, which burn injury prediction is based on, only goes out 50 seconds (which is too short).

To provide some perspective on these results, Jeff Stull conducted similar testing for the US Fire Administration several years ago using this technique. Using a conventional fire resistant composite with a 7.5 oz PBI/Kevlar outer shell, 3.9 oz Crosstech E89 moisture barrier, 7.8 oz 3 layer E89 Nomex facecloth thermal barrier, a time-to-pain of 91 seconds and time-to-burn of 135 seconds were observed under dry conditions, and 85 seconds (pain) and 115 seconds (burn) under wet conditions. The wet conditions were produced by immersing the fabric for 2 minutes, hang drying for 10 minutes, and then blotting under 0.5 psi for 20 minutes.

When Hydroweave was wet tested using the same radiant energy level, there was an average time-to-pain of 152.3 seconds and time-to-burn of 256.3. This represents almost 70% better protection times over conventional fire protection products. In addition, the conventional product weighed over 16 oz per square yard dry, while this version of Hydroweave weighed in at only 10.3 oz per yard activated (wet).

While a 7.5 oz shell is typically used for fire resistant products, these tests were all achieved using a lightweight 4.5 oz shell fabric. The TPP rating of 27.1 fell short of the NFPA TPP requirement of 35 prompting AquaTex to submit 7.5 oz variant of the Hydroweave for test. When the outer shell of Hydroweave is thickened, we expect that all TPP ratings will show an even greater increase over conventional flame resistant products. The 7.5 oz shells are fairly standard throughout the fire service for protective clothing due to their increased durability and physical hazard resistance.

Like anything else, buy all the safety you can afford
Ask Dale Earnhart Jr. He will tell you all about not wearing underwear under your suit. Look back to a 2004 crash in a Corvette if you do not know what I am taking about. If you crash and catch fire I think you will find a 3.2A/5 rating to short of time.
Steelhorse said:
Ask Dale Earnhart Jr. He will tell you all about not wearing underwear under your suit. Look back to a 2004 crash in a Corvette if you do not know what I am taking about. If you crash and catch fire I think you will find a 3.2A/5 rating to short of time.

Maybe, I said in my opening statement that you need to "exceed" the 3.2A/5 rating, by adding underwear to that rating you would "up" the rating to something else, but again, you have more garments to deal with, it would be better to buy a 3.2A/10 (or higher) than use a 3.2A/5 and add underwear. Another thing is that underwear is closer to the skin, so there is no air space between the underwear and the skin which provides a thermal barrier. This air space is crucial to providing protection to the wearer. IMO adding underwear to a suit, when an equivalent suit is available, is problematic for the reasons I've already listed.

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