Methods of Insulating Air Ducts and Joints with Black Rubber Insulation

This article explains how to insulate air ducts with black rubber insulation for air ducts, chilled water pipes, joints and valves to maintain the temperature of refrigerant or chilled water in pipes and prevent condensation. Therefore, insulation is extremely important for both aesthetic appeal and insulation efficiency.

Incorrect insulation installation wastes both effort and time. Sometimes damaged insulation or air conditioning damage requires system removal or work rejection. Selecting quality insulation and proper installation are therefore critical factors.

If you want to know more details about black rubber insulation, types of black rubber insulation, and other applications, you can read more at

When cutting, keep the blade sharp with an acute angle for scoring the insulation (avoid holding the knife handle too high).

To make holes in insulation, use a pipe to punch holes in the insulation.

Cut black rubber insulation on a smooth surface.

When installing tubular air duct insulation, we can slip it over pipes and slide it into various joints.

Do not attempt to force insulation around tight corners as this may cause the insulation to tear.

However, in some cases where corners are very tight and we force the insulation around narrow corners, it will cause the insulation to wrinkle and form ridges, reducing the thickness in that area from the calculated amount. When insulation thickness decreases, there is a risk of condensation in that area, leading to damage to pipes and insulation.

1. Use a sharp knife to slit the air duct insulation along its entire length
2. Fit the insulation over the pipe to be installed and apply adhesive to both sides of the slit edges

3. Allow the adhesive to dry. You can test by touching the glued area with your finger
4. Press the insulation edges together to bond them

For the first layer of tubular insulation, we select the inner diameter size according to the pipe’s outer diameter. For the second layer, we select according to the O.D. of the first layer rubber insulation.

I.D. of layer 2 = O.D. of layer 1

If the pipe diameter after insulation wrapping is sufficiently large, we recommend using sheet-type black rubber insulation for the second layer because we can cut sheet insulation to fit the exact size of the first layer pipe.

In some cases where the OD pipe size is larger than 3 inches (89 mm), we can choose to use rubber sheet insulation for wrapping.

At the ends of the pipe insulation wrapping, it must be sealed with adhesive to fit tightly against the first layer insulation to prevent insulation sagging and internal air gaps. If the pipe is larger than 24 inches (600 mm), we must apply adhesive over the entire surface of both the first and second layer insulation during installation to prevent CUI (Corrosion under insulation).

In cases where we apply multi-layer insulation, for layer 1 we apply adhesive over the entire pipe surface and the entire insulation sheet before installation. For layer 2, it must wrap tightly against the first layer, requiring adhesive application over the entire surface of the previous layer and the second layer insulation sheet.

At joint areas marked with yellow lines, we wrap by overlapping joints, and every joint must be sealed with insulation adhesive.

Cutting various joints can use the patterns drawn on ArmaFlex Class1 black rubber insulation boxes, including cuts at 11.25°, 15°, 22.5° and 45° which cover practical applications.

Cutting at 45° angles along yellow lines allows installation at 90° angles.

Cutting at 22.5° angles along yellow lines allows installation at 45° angles.

Cutting at 22.5° angles along yellow lines at 2 positions allows installation at 90° angles with 1 middle piece.

Cutting at 15° angles along yellow lines at 3 positions allows installation at 90° angles with 2 middle pieces.

Cutting at 11.25° angles along yellow lines at 4 positions allows installation at 90° angles with 3 middle pieces.

We cut two 90° elbows and cut them again at 45° angles at the elbow corners along the yellow lines in the image.

We cut two 45° elbows and one 90° elbow, then use insulation adhesive to attach the cut elbows as shown in the image, cut the corners off the 90° elbow, and attach straight pipe insulation with insulation adhesive.

Cut two 90° bends and split the pipe along the middle following the yellow line, then use insulation adhesive to bond both pieces together.

1. Punch a hole in the insulation area where installation is required using a pipe of the same size.
2. Carve out the insulation material to form a semicircle along the yellow line.
3. Use insulation adhesive to seal the joint areas to complete the work.

1. Cut the black rubber insulation at the end of the branch pipe at a 45° angle.
2. Cut the black rubber insulation at the main pipe area at a 90° angle.
3. Connect the grooved insulation pieces together with insulation adhesive.

1. The inner diameter size of insulation covering the joint equals the original pipe size + thickness of installed insulation. For example, 10 mm pipe with 19 mm thick insulation requires joint insulation of 48 mm size with 19 mm thick insulation.
2. Wrap joint insulation with approximately 25 mm overlap with straight pipe insulation.
3. Use insulation adhesive to seal the ends in the overlapping areas.

1. The insulation used to wrap threaded joints uses tubular insulation sized equal to the O.D. of the threaded joint with minimum length of 40 mm on each side from the threaded joint connection.
2. For pipes larger than 35 mm, cut the insulation material at the insulation ends into wedge shapes and wrap tightly against the straight pipe, then use adhesive to seal the joint areas.

1. Use a pipe with sharp end to punch holes in insulation along the wrapping direction

2. Cut the branch pipe insulation at 45° angle and carve the insulation end into a semicircle
3. Use insulation adhesive to attach the branch pipe and main pipe together

1. Cut the branch pipe insulation at 45° angle along the yellow line

2. Cut the other side insulation at 22.5° angle
3. Use adhesive to seal the branch pipe insulation to the main pipe

If the pipe diameter exceeds 500 mm, adhesive should be applied to the underside of the pipe to prevent insulation vibration.

Find the elbow radius and pipe circumference to be wrapped, and cut insulation according to the pattern below.

r = elbow radius (mm)
1/2 C = half of pipe circumference (mm)
t’ = insulation thickness (mm)

Cut insulation according to the first drafted pattern, then use the first piece as a template for cutting the second piece.

Apply adhesive to the outer edges of insulation and bond both pieces together.

Start bonding from the end areas first, then the middle, then press all parts to bond together.

Apply adhesive to the inner edges and set aside for installation.

Install insulation and seal joint areas with adhesive.

1. Use a pipe with sharp end to punch holes in insulation along the wrapping direction

Split the insulation end into wedge shape and connect the split areas with adhesive.

Cut the insulation end to equal the reducer length.

Use adhesive to seal all joints in the insulation wrapping to finish the work.

1. Find the elbow radius and pipe circumference to be wrapped, and cut insulation according to the pattern below

2. Cut elbow insulation template

r = elbow radius (mm)
1/2 C = half of pipe circumference (mm)
t’ = insulation thickness (mm)

3. Cut insulation according to the first drafted pattern, then use the first piece as a template for cutting the second piece

4. Apply adhesive to the outer edges of insulation and bond both pieces together

5. Start bonding from the end areas first, then the middle, then press all parts to bond together

6. Apply adhesive to the inner edges and set aside for installation

7. Install insulation and seal joint areas with adhesive

After wrapping pipes up to the valve section, we need to wrap the valve with black rubber sheet insulation as well.

1. Measure dimensions to cut black rubber to wrap the valve

• D1 = valve flange face diameter
• D2 = diameter of black rubber insulation pipe wrapped up to the valve

2. Cut black rubber sheet into circles and wrap over the pipe

• Cut black rubber sheet into circles with outer diameter equal to D1 and inner diameter equal to D2.
• Use the cut black rubber sheet ring to wrap over the pipe with black rubber adhesive.

3. Measure valve dimensions for black rubber insulation wrapping

• h = height measured from outer edge of lower ring insulation sheet to outer edge at top
• a = valve neck diameter
• c = circumference of ring insulation sheet wrapping the valve

4. Method of cutting insulation sheet to wrap valve neck

• Use measurements h, a, c from measurements to cut on black rubber insulation sheet.

5. After cutting the insulation sheet, wrap it over the valve body and secure with black rubber adhesive.

1. Measure distances h and B to cut insulation sheet

• h = valve neck flange height
• B = valve neck flange height

2. Wrap the cut insulation sheet to attach to valve stem and measure distances for valve neck wrapping

• a = shortest distance from valve neck base to valve stem insulation sheet
• C = circumference of valve stem insulation sheet

3. Draft pattern to cut on black rubber insulation sheet

• After obtaining distances a and C, we use both measurements to draft the pattern on insulation sheet.
• Divide circumference C into 4 equal parts.
• This gives us 5 red straight lines total. Designate lines 2 and 3 to have length equal to valve stem a.
• At the tops of lines 2 and 4, draw circles with size equal to valve radius (radius of circumference C).
• Draw circles at distance a of every line (as shown in the image above).

4. Use knife to cut along points where circle radii intersect

• Use knife to cut along the lines where radii intersect.

5. Trim cut edges for appearance and wrap with insulation sheet

• Trim edges of black rubber insulation sheet.
• Apply black rubber adhesive to insulation sheet edges then wrap around valve stem.

6. Apply adhesive to finish valve insulation sheet details

• Apply adhesive along joint edges to bond with other insulation parts and press insulation together.

1. Measure valve height and valve width

• L = valve length + (2 x insulation thickness)
• H = valve height + (2 x insulation thickness)
• W = valve diameter + 10 mm

2. Measure dimensions and cut insulation sheet

• Use sharp knife to cut insulation as shown in image with 2 types of curved sheets and 1 rectangular sheet.

3. Use black adhesive on insulation sheet for valve box assembly

4. After adhesive completely dries, assemble all 3 insulation pieces together

5. Use black rubber insulation cord to measure black rubber box for insulation wrapping

• Use insulation cord with thickness equal to insulation used for valve box wrapping, measure length around valve box.
• Use measured distance to cut black rubber insulation sheet with width equal to valve width and length equal to valve box circumference.

6. Apply adhesive around black rubber insulation sheet, wait for adhesive to dry then assemble together

7. Use pointed knife to punch holes in insulation box for pipe fitting

1. Use black rubber insulation strip to measure pipe circumference and use measuring tape to measure elbow height

• A = inward bend height
• B = outward bend height
• C = pipe circumference

2. Use measured distances to draft pattern on black rubber insulation sheet

• Divide circumference C into 2 parts to get 3 straight lines total.
• Use compass to draw circles with radius B along divided straight lines to get 3 circles total.

3. Use compass to draw curved lines according to pattern and use knife to score along intersecting lines

4. Apply black adhesive to both cut insulation pieces and assemble with elbow

5. Wrap black rubber insulation elbow

Insulation methods for strainers and seat valves are very similar.

1. Use black rubber insulation strip to measure insulated pipe diameter, valve, and insulated pipe circumference

• D1 = valve flange face diameter
• D2 = outer diameter of black rubber insulated pipe
• C = black rubber insulated pipe circumference

2. Cut insulation sheet to wrap over insulated pipe and measure valve dimensions

• Cut insulation into circles to wrap over black rubber insulated pipe.
• Measure dimensions h, a1, a2, e, D3.
  • h = valve height from flange face to flange face
  • a1 = distance from flange face to lower strainer
  • a2 = distance from flange face to upper strainer
  • e = strainer shoulder width
  • D3 = strainer valve neck diameter

3. Pattern for cutting black rubber insulation to wrap valve body

• Measure distances and cut black rubber insulation sheet according to image for valve wrapping.

4. After wrapping valve body, cut insulation sheet into circles to wrap valve neck

5. Measure distances for valve neck wrapping

• a = shortest distance between insulation sheet and valve body
• b = longest distance between insulation sheet and valve body

6. Cut insulation sheet according to image for valve neck wrapping

7. Wrap cut insulation sheet to connect with valve body

1. Measure flange width and flange circumference

• Use vernier calipers to measure flange width from bolt head to bolt head on opposite side plus thickness of black rubber insulation on both sides.
• Use black rubber insulation strip to measure flange circumference.
• Measure flange diameter.

2. Cut insulation sheet according to measured dimensions

• 2 circular sheets sized equal to flange diameter
• 1 rectangular sheet
  • Width = bolt head distance from flange on both sides + (2 x black rubber insulation thickness)
  • Length = flange circumference length

3. Apply adhesive and attach all 3 pieces together according to image

4. Split flange insulation box along length direction and carve interior according to pipe size

In installing air duct, chilled water pipe, joint, and elbow insulation, proper installation methods should be followed to ensure insulation can be used for a long time at full efficiency, reducing problems and other costs that may follow.