FUSION Issue 3-2026 DIGITAL - Flipbook - Page 25
THE VACUUM BAG
The blue film being peeled back here is the vacuum bag. It seals the entire
laminate stack against the mould, creating an airtight envelope. When a
vacuum pump draws the air out, atmospheric pressure bears down on the
stack from above – compacting the layers and driving resin through the
reinforcement evenly. Without it, there is no infusion.
THE PEEL PLY
The woven fabric visible directly beneath the bag is peel ply. It does not
become part of the finished component. Its job is to protect the laminate
surface during cure and leave a clean, chemically active texture when it
is stripped away. That texture is what allows the next process – whether
bonding, painting, or fairing – to adhere properly. The quality of the bond
starts here.
THE CARBON FIBRE
The dark weave visible at the centre is the structural reinforcement: carbon
fibre fabric, laid up in calculated orientations to carry load in the directions
the finished part demands. The weave pattern, the number of plies, and the
fibre angle are all engineering decisions made long before the bag goes on.
This is what the rest of the stack exists to protect and consolidate.
THE SEALANT TAPE
The green tacky material at the edges is sealant tape, sometimes called
tacky tape or mastic tape. It forms the airtight seal between the vacuum
bag and the mould surface. A bag that holds vacuum perfectly at the
start of an infusion and loses it halfway through is usually a sealant tape
problem. Getting the seal right is not complicated. It is just not optional.
THE STACK IS A SYSTEM
Each layer in a vacuum infusion stack has a specific function, and each
depends on the others performing correctly. A perfect bag over a poorly laid
reinforcement produces a poor part. A well-laid reinforcement under a leaking
bag produces the same result. The finished component carries no trace of this
process – but every decision made here is locked into it permanently.
BY THE TIME THE PART LEAVES THE
MOULD, NONE OF THIS IS VISIBLE.
BUT ALL OF IT IS STILL THERE.
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