Towpregs are pre-impregnated reinforcement fibers wound on spools and then further processed. 

The advantages such are:

  • Faster winding speed
  • More consistent part resin content
  • Access to carbon fiber choices in small quantities
  • Elimination of “Dry Fly” carbon fibers in working environment
  • Much cleaner process than wet winding

Filament winding is a composite manufacturing process which involves applying filament tows such as fiber glass or carbon fiber onto a mandrel. The filament layers are cross plied to achieve the strength characteristics determined by the part designer. The applied tows can be combined with a resin matrix immediately prior to application to the mandrel (wet winding) or the tows can be a towpreg which is a fiber/resin combination made by a vendor.

Filament winding process

Wet winding is commonly used to make a wide range of products such as pipe, transmission poles, gas pressure bottles, liquid pressure vessels, etc. Generally, these applications do not require heat curing and the range of resin content of the part is wide. Usually, external pressure is not applied during cure. The process is mature and widely accepted. However, it can be messy, and employees are exposed to fumes of catalyzed resin and, dry fiber “fly”, and solvents.

Carbon Fiber Roll Wrapping Machine

Towpreg winding is used to make parts which require a narrow resin content range. The resin/fiber tows are generally processed at higher speeds compared to wet winding. The resulting fiber volume of the wound parts can be higher and more precisely controlled.  The cost per pound of material is higher than wet winding. However, the cost of applied material is improved by more precise tow placement at higher speed. Also, clean-up of towpreg winding is minimal. Towpreg winding usually employs carbon fiber tows and resins with heat resistance properties. Also, part design is likely weight critical.

Mitsubishi manufactures a range of carbon fibers which are incorporated in FTM Towpreg products for a variety of applications. 3K, 12K and 24K tow sizes are available.

HMT301General Purpose, toughened towpreg, controlled flow with versatile processing.
HMT316Flame retardant, toughened towpreg designed for electrical applications
HMT317General purpose towpreg.
HMT321High temperature resistance, toughened
HMT321FRHigh Tg towpreg with flame retardency.
HMT4030Flame retardant meets FAR25.853
HMT507Towpreg designed for pressure vessels. Cures at 205°F, in polyethylene’s limits
HMT5300Low temperature variable cure towpreg with long out-time.
HMT6600Highly toughened, high temperature cure towpreg. 350°F Cure, high temperature resistance

The technical data sheets are located at 

Give Northern a call to discuss your application, identify the right towpreg for your application and request a sample.