Calculate blow-up ratio (BUR) for blown film from die diameter and layflat width or bubble diameter, or solve for layflat width, die size or film gauge.

Width of the flattened tube. It is half the bubble circumference, so bubble diameter = 2 × layflat ÷ π.

Die gap, film gauge and resin

Enter with the die gap to get the draw down ratio (DDR).

Optional. Checks your BUR against the typical range for that resin.

Blow-Up Ratio Formula

The following equation is used to calculate a Blow-Up Ratio.

BR = Df / Dd
  • Where BR is the Blow-Up Ratio
  • Df is the final tube diameter
  • Dd is the die diameter

To calculate a Blow-Up Ratio, divide the final tube diameter by the die diameter.

What is Blow-Up Ratio?

Definition:

A blow-up ratio is a term used in blown film problems to describe the ratio of the final tube diameter to the die diameter.

How to calculate Blow-Up Ratio?

Example Problem:

The following example outlines how to calculate a Blow-Up Ratio.

First, determine the diameter of the die. In this example, the die being used is measured to have a diameter of 5 inches.

Next, determine the final tube diameter. The final tube diameter made with this die yields a diameter of 6 inches.

Finally, calculate the Blow-Up Ratio using the formula above:

BR = Df / Dd

BR = 6 / 5

BR = 1.2